docs: add install instructions and Kuma migration guide to README

Supports `goupkeep version`, `--version`, and `-v`. Prints version,
commit hash, and build date when injected via ldflags. Shows "dev"
for local builds. Dockerfile updated with ARGs for version injection.

.gitea/workflows/ci.yml

@@ -0,0 +1,41 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: sh
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.24"
+
+      - name: Install build tools
+        run: apk add --no-cache gcc musl-dev
+
+      - name: Vet
+        run: go vet ./...
+
+      - name: Test
+        run: CGO_ENABLED=1 go test -race -timeout 120s ./...
+
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.24"
+
+      - uses: golangci/golangci-lint-action@v7
+        with:
+          version: v2.11.2

.golangci.yml

@@ -0,0 +1,29 @@
+version: "2"
+
+linters:
+  default: none
+  enable:
+    - errcheck
+    - staticcheck
+    - govet
+    - gosec
+    - ineffassign
+    - unused
+
+  settings:
+    errcheck:
+      check-type-assertions: false
+      check-blank: false
+
+  exclusions:
+    presets:
+      - std-error-handling
+      - common-false-positives
+    rules:
+      - path: _test\.go
+        linters:
+          - errcheck
+          - gosec
+
+run:
+  timeout: 5m

CHANGELOG.md

@@ -0,0 +1,46 @@
+# Changelog
+
+## [2026.05.2] — 2026-05-23
+
+### Added
+- Comprehensive test suite (94 tests across monitor, server, cluster)
+- golangci-lint config with CI enforcement
+- Gitea Actions CI pipeline (test + lint)
+- Graceful shutdown for HTTP and SSH servers
+- Context-aware alert delivery with timeout
+- Request size limits on all POST endpoints
+- Constant-time secret comparison
+- Check interval jitter to prevent thundering herd
+- `--version` flag with build metadata injection
+
+### Fixed
+- Silent JSON unmarshal failures in alert settings
+- Panic on crypto/rand failure replaced with error return
+- Alert delivery errors now logged instead of swallowed
+- log.Fatalf in goroutines replaced with log.Printf
+- Deprecated LineUp/LineDown API calls
+
+### Security
+- Cluster secret compared with crypto/subtle (timing-safe)
+- http.MaxBytesReader on all JSON endpoints
+- ReadHeaderTimeout added to HTTP server
+
+## [2026.05.1] — 2026-05-14
+
+### Added
+- Distributed probing with leader + probe nodes
+- Config-as-code (YAML apply/export with dry-run, prune)
+- TUI visual polish (zebra striping, sparklines, breadcrumbs)
+- Incident management and maintenance windows
+- 9 alert providers (Discord, Slack, Email, Ntfy, Telegram, PagerDuty, Pushover, Gotify, Webhook)
+
+## [2026.04.1] — Initial independent fork
+
+### Added
+- SSH-accessible TUI (Bubble Tea + Wish)
+- 6 check types (HTTP, Push, Ping, Port, DNS, Group)
+- SQLite and PostgreSQL support
+- HA clustering with automatic failover
+- Prometheus metrics endpoint
+- Public status page
+- Uptime Kuma import

CONTRIBUTING.md

@@ -0,0 +1,23 @@
+# Contributing
+
+## Development
+
+```sh
+go run cmd/goupkeep/main.go -demo  # starts with sample data
+ssh -p 23234 localhost              # connect to TUI
+```
+
+## Tests
+
+```sh
+go test ./...              # unit tests
+go test -race ./...        # race detector
+golangci-lint run ./...    # linting
+```
+
+## Pull Requests
+
+- Branch from `main`, PR back to `main`
+- Conventional Commits for messages (`feat:`, `fix:`, `chore:`)
+- Tests must pass, linter must be clean
+- One logical change per PR

Dockerfile

@@ -6,7 +6,10 @@ COPY go.mod go.sum ./
 RUN go mod download
 COPY . .
 ENV CGO_ENABLED=1
-RUN go build -ldflags="-s -w" -o go-upkeep ./cmd/goupkeep/main.go
+ARG VERSION=dev
+ARG COMMIT=none
+ARG BUILD_DATE=unknown
+RUN go build -ldflags="-s -w -X main.version=${VERSION} -X main.commit=${COMMIT} -X main.date=${BUILD_DATE}" -o go-upkeep ./cmd/goupkeep/main.go
 
 # --- Stage 2: Runner ---
 FROM alpine:latest

LICENSE

@@ -1,6 +1,7 @@
 MIT License
 
 Copyright (c) 2026 Roman Dvořák
+Copyright (c) 2026 Tyler Koenig
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -2,7 +2,7 @@
 
 Self-hosted uptime monitor with a TUI you can access over SSH. No browser, no install on the client — just `ssh -p 23234 your-server`.
 
-Originally forked from [RDGames/go-upkeep](https://github.com/RDGames/go-upkeep). This is an independent fork with significant additions.
+Built on the foundation of [RDGames/go-upkeep](https://github.com/RDGames/go-upkeep).
 
 ## What it does
 
@@ -28,6 +28,25 @@ Seed some demo data to see it in action:
 go run cmd/goupkeep/main.go -demo
 ```
 
+## Install
+
+### From source
+
+```bash
+go install gitea.lerkolabs.com/lerko/uptime/cmd/goupkeep@latest
+```
+
+### Docker
+
+```bash
+docker pull lerko/go-upkeep:latest
+docker run -p 23234:23234 -p 8080:8080 -v ./data:/data lerko/go-upkeep
+```
+
+### Binary
+
+Download from [Releases](https://gitea.lerkolabs.com/lerko/uptime/releases).
+
 ## Config as code
 
 Export your current monitors:
@@ -85,6 +104,17 @@ First run: attach to the container (`docker attach go-upkeep`), go to the Users
 | `UPKEEP_CLUSTER_SECRET` | | Shared key for cluster + API auth |
 | `UPKEEP_INSECURE_SKIP_VERIFY` | `false` | Skip TLS verification for checks |
 
+## Migrating from Uptime Kuma
+
+Export your Kuma backup JSON, then:
+
+```bash
+curl -X POST http://localhost:8080/api/import/kuma \
+  -H "X-Upkeep-Secret: your-secret" \
+  -H "Content-Type: application/json" \
+  -d @kuma-backup.json
+```
+
 ## License
 
 MIT — see [LICENSE](LICENSE).

SECURITY.md

@@ -0,0 +1,19 @@
+# Security Policy
+
+## Reporting a Vulnerability
+
+If you find a security issue, please email security@lerkolabs.com rather than opening a public issue.
+
+Include:
+- Description of the vulnerability
+- Steps to reproduce
+- Potential impact
+
+We'll acknowledge within 48 hours and aim to patch within 7 days for critical issues.
+
+## Scope
+
+- SSH server authentication
+- Cluster API authentication
+- Stored credentials (alert provider tokens)
+- Status page information leakage

cmd/goupkeep/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"go-upkeep/internal/cluster"
@@ -17,6 +18,7 @@ import (
 	"os/signal"
 	"strconv"
 	"syscall"
+	"time"
 
 	tea "github.com/charmbracelet/bubbletea"
 	"github.com/charmbracelet/ssh"
@@ -25,6 +27,12 @@ import (
 	"github.com/mattn/go-isatty"
 )
 
+var (
+	version = "dev"
+	commit  = "none"
+	date    = "unknown"
+)
+
 func main() {
 	log.SetOutput(os.Stderr)
 
@@ -36,11 +44,22 @@ func main() {
 		case "export":
 			runExport(os.Args[2:])
 			return
+		case "version", "--version", "-v":
+			printVersion()
+			return
 		}
 	}
 	runServe(os.Args[1:])
 }
 
+func printVersion() {
+	if version == "dev" {
+		fmt.Println("go-upkeep dev")
+	} else {
+		fmt.Printf("go-upkeep %s (%s, %s)\n", version, commit, date)
+	}
+}
+
 func envOrDefault(key, fallback string) string {
 	if v := os.Getenv(key); v != "" {
 		return v
@@ -74,7 +93,7 @@ func runApply(args []string) {
 	prune := fs.Bool("prune", false, "Delete monitors/alerts not in YAML")
 	dbType := fs.String("db-type", envOrDefault("UPKEEP_DB_TYPE", "sqlite"), "Database type")
 	dsn := fs.String("dsn", envOrDefault("UPKEEP_DB_DSN", "upkeep.db"), "Database DSN")
-	fs.Parse(args)
+	_ = fs.Parse(args) // ExitOnError: parse errors exit before returning
 
 	if *filePath == "" {
 		fmt.Fprintln(os.Stderr, "error: -f flag is required")
@@ -107,7 +126,7 @@ func runExport(args []string) {
 	outPath := fs.String("o", "-", "Output file path (- for stdout)")
 	dbType := fs.String("db-type", envOrDefault("UPKEEP_DB_TYPE", "sqlite"), "Database type")
 	dsn := fs.String("dsn", envOrDefault("UPKEEP_DB_DSN", "upkeep.db"), "Database DSN")
-	fs.Parse(args)
+	_ = fs.Parse(args) // ExitOnError: parse errors exit before returning
 
 	s := openStore(*dbType, *dsn)
 
@@ -184,6 +203,7 @@ func runServe(args []string) {
 		fmt.Printf("Cluster: Running as PROBE (node=%s, region=%s)\n", nodeID, nodeRegion)
 
 		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
 		done := make(chan os.Signal, 1)
 		signal.Notify(done, os.Interrupt, syscall.SIGINT, syscall.SIGTERM)
 		go func() {
@@ -210,7 +230,7 @@ func runServe(args []string) {
 	flagDSN := fs.String("dsn", dbDSN, "Database DSN")
 	demo := fs.Bool("demo", false, "Seed demo data")
 	importKuma := fs.String("import-kuma", "", "Import Uptime Kuma backup JSON file")
-	fs.Parse(args)
+	_ = fs.Parse(args) // ExitOnError: parse errors exit before returning
 
 	var s store.Store
 	var dbErr error
@@ -225,6 +245,7 @@ func runServe(args []string) {
 		fmt.Printf("Database connection error: %v\n", dbErr)
 		os.Exit(1)
 	}
+	defer s.Close()
 
 	if err := s.Init(); err != nil {
 		fmt.Printf("Database init error: %v\n", err)
@@ -263,7 +284,7 @@ func runServe(args []string) {
 	eng.InitLogs()
 	eng.Start(ctx)
 
-	server.Start(server.ServerConfig{
+	httpSrv := server.Start(server.ServerConfig{
 		Port:         httpPort,
 		EnableStatus: enableStatus,
 		Title:        statusTitle,
@@ -276,7 +297,7 @@ func runServe(args []string) {
 		SharedKey: clusterKey,
 	}, eng)
 
-	startSSHServer(*port, s, eng)
+	sshSrv := startSSHServer(*port, s, eng)
 
 	if isatty.IsTerminal(os.Stdout.Fd()) || isatty.IsCygwinTerminal(os.Stdout.Fd()) {
 		p := tea.NewProgram(tui.InitialModel(true, s, eng), tea.WithAltScreen(), tea.WithMouseCellMotion())
@@ -291,9 +312,22 @@ func runServe(args []string) {
 		fmt.Println("Shutting down...")
 	}
 	cancel()
+
+	shutdownCtx, shutdownCancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer shutdownCancel()
+	if httpSrv != nil {
+		if err := httpSrv.Shutdown(shutdownCtx); err != nil {
+			log.Printf("HTTP shutdown error: %v", err)
+		}
+	}
+	if sshSrv != nil {
+		if err := sshSrv.Shutdown(shutdownCtx); err != nil {
+			log.Printf("SSH shutdown error: %v", err)
+		}
+	}
 }
 
-func startSSHServer(port int, db store.Store, eng *monitor.Engine) {
+func startSSHServer(port int, db store.Store, eng *monitor.Engine) *ssh.Server {
 	s, err := wish.NewServer(
 		wish.WithAddress(fmt.Sprintf(":%d", port)),
 		wish.WithHostKeyPath(".ssh/id_ed25519"),
@@ -308,13 +342,14 @@ func startSSHServer(port int, db store.Store, eng *monitor.Engine) {
 	)
 	if err != nil {
 		fmt.Printf("SSH server error: %v\n", err)
-		return
+		return nil
 	}
 	go func() {
-		if err := s.ListenAndServe(); err != nil {
+		if err := s.ListenAndServe(); err != nil && !errors.Is(err, ssh.ErrServerClosed) {
-			log.Fatalf("SSH server failed: %v", err)
+			log.Printf("SSH server error: %v", err)
 		}
 	}()
+	return s
 }
 
 func seedDemoData(s store.Store) {
@@ -324,13 +359,22 @@ func seedDemoData(s store.Store) {
 	}
 	fmt.Println("Seeding demo data...")
 
-	s.AddAlert("Discord Ops", "discord", map[string]string{"url": "https://discord.com/api/webhooks/demo/token"})
+	if err := s.AddAlert("Discord Ops", "discord", map[string]string{"url": "https://discord.com/api/webhooks/demo/token"}); err != nil {
-	s.AddAlert("Slack Infra", "slack", map[string]string{"url": "https://hooks.slack.com/services/DEMO/WEBHOOK"})
+		log.Printf("demo seed: add alert: %v", err)
-	s.AddAlert("Email Oncall", "email", map[string]string{
+		return
+	}
+	if err := s.AddAlert("Slack Infra", "slack", map[string]string{"url": "https://hooks.slack.com/services/DEMO/WEBHOOK"}); err != nil {
+		log.Printf("demo seed: add alert: %v", err)
+		return
+	}
+	if err := s.AddAlert("Email Oncall", "email", map[string]string{
 		"host": "smtp.example.com", "port": "587",
 		"user": "oncall@example.com", "pass": "replace-me",
 		"from": "oncall@example.com", "to": "team@example.com",
-	})
+	}); err != nil {
+		log.Printf("demo seed: add alert: %v", err)
+		return
+	}
 
 	alerts, _ := s.GetAllAlerts()
 	alertID := 0
@@ -338,16 +382,23 @@ func seedDemoData(s store.Store) {
 		alertID = alerts[0].ID
 	}
 
-	s.AddSite(models.Site{Name: "Google", URL: "https://www.google.com", Type: "http", Interval: 30, AlertID: alertID, CheckSSL: true, ExpiryThreshold: 14, MaxRetries: 2})
+	demoSites := []models.Site{
-	s.AddSite(models.Site{Name: "GitHub", URL: "https://github.com", Type: "http", Interval: 30, AlertID: alertID, CheckSSL: true, ExpiryThreshold: 7, MaxRetries: 3})
+		{Name: "Google", URL: "https://www.google.com", Type: "http", Interval: 30, AlertID: alertID, CheckSSL: true, ExpiryThreshold: 14, MaxRetries: 2},
-	s.AddSite(models.Site{Name: "Cloudflare DNS", URL: "https://1.1.1.1", Type: "http", Interval: 60, AlertID: alertID, ExpiryThreshold: 7, MaxRetries: 1})
+		{Name: "GitHub", URL: "https://github.com", Type: "http", Interval: 30, AlertID: alertID, CheckSSL: true, ExpiryThreshold: 7, MaxRetries: 3},
-	s.AddSite(models.Site{Name: "JSON Placeholder", URL: "https://jsonplaceholder.typicode.com/posts/1", Type: "http", Interval: 45, AlertID: alertID, ExpiryThreshold: 7, MaxRetries: 2})
+		{Name: "Cloudflare DNS", URL: "https://1.1.1.1", Type: "http", Interval: 60, AlertID: alertID, ExpiryThreshold: 7, MaxRetries: 1},
-	s.AddSite(models.Site{Name: "Nonexistent Site", URL: "https://this-domain-does-not-exist-12345.com", Type: "http", Interval: 30, AlertID: alertID, ExpiryThreshold: 7, MaxRetries: 3})
+		{Name: "JSON Placeholder", URL: "https://jsonplaceholder.typicode.com/posts/1", Type: "http", Interval: 45, AlertID: alertID, ExpiryThreshold: 7, MaxRetries: 2},
-	s.AddSite(models.Site{Name: "Bad Port", URL: "https://localhost:19999", Type: "http", Interval: 30, ExpiryThreshold: 7, MaxRetries: 1})
+		{Name: "Nonexistent Site", URL: "https://this-domain-does-not-exist-12345.com", Type: "http", Interval: 30, AlertID: alertID, ExpiryThreshold: 7, MaxRetries: 3},
-	s.AddSite(models.Site{Name: "Backup Cron", Type: "push", Interval: 300, AlertID: alertID, ExpiryThreshold: 7})
+		{Name: "Bad Port", URL: "https://localhost:19999", Type: "http", Interval: 30, ExpiryThreshold: 7, MaxRetries: 1},
-	s.AddSite(models.Site{Name: "DB Healthcheck", Type: "push", Interval: 120, AlertID: alertID, ExpiryThreshold: 7})
+		{Name: "Backup Cron", Type: "push", Interval: 300, AlertID: alertID, ExpiryThreshold: 7},
-	s.AddSite(models.Site{Name: "Gateway", Type: "ping", Interval: 30, AlertID: alertID, Hostname: "10.0.0.1", Timeout: 5, ExpiryThreshold: 7})
+		{Name: "DB Healthcheck", Type: "push", Interval: 120, AlertID: alertID, ExpiryThreshold: 7},
-	s.AddSite(models.Site{Name: "SSH Server", Type: "port", Interval: 60, AlertID: alertID, Hostname: "10.0.0.1", Port: 22, Timeout: 5, ExpiryThreshold: 7})
+		{Name: "Gateway", Type: "ping", Interval: 30, AlertID: alertID, Hostname: "10.0.0.1", Timeout: 5, ExpiryThreshold: 7},
+		{Name: "SSH Server", Type: "port", Interval: 60, AlertID: alertID, Hostname: "10.0.0.1", Port: 22, Timeout: 5, ExpiryThreshold: 7},
+	}
+	for _, site := range demoSites {
+		if err := s.AddSite(site); err != nil {
+			log.Printf("demo seed: add site %q: %v", site.Name, err)
+		}
+	}
 }
 
 func isKeyAllowed(db store.Store, incomingKey ssh.PublicKey) bool {

docker-compose.yml

@@ -0,0 +1,18 @@
+services:
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: upkeep
+    restart: unless-stopped
+    ports:
+      - "23234:23234"
+      - "8080:8080"
+    environment:
+      - UPKEEP_DB_TYPE=sqlite
+      - UPKEEP_DB_DSN=/data/upkeep.db
+      - UPKEEP_HTTP_PORT=8080
+      - UPKEEP_STATUS_ENABLED=true
+      - UPKEEP_STATUS_TITLE=System Status
+    volumes:
+      - ./data:/data

internal/alert/alert.go

@@ -2,6 +2,7 @@ package alert
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"fmt"
 	"go-upkeep/internal/models"
@@ -15,7 +16,7 @@ import (
 var alertClient = &http.Client{Timeout: 10 * time.Second}
 
 type Provider interface {
-	Send(title, message string) error
+	Send(ctx context.Context, title, message string) error
 }
 
 type PayloadFunc func(title, message string) ([]byte, error)
@@ -25,12 +26,17 @@ type HTTPProvider struct {
 	Payload PayloadFunc
 }
 
-func (h *HTTPProvider) Send(title, message string) error {
+func (h *HTTPProvider) Send(ctx context.Context, title, message string) error {
 	body, err := h.Payload(title, message)
 	if err != nil {
 		return err
 	}
-	resp, err := alertClient.Post(h.URL, "application/json", bytes.NewBuffer(body))
+	req, err := http.NewRequestWithContext(ctx, "POST", h.URL, bytes.NewBuffer(body))
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	resp, err := alertClient.Do(req)
 	if err != nil {
 		return err
 	}
@@ -170,7 +176,12 @@ type EmailProvider struct {
 	Host, Port, User, Pass, To, From string
 }
 
-func (e *EmailProvider) Send(title, message string) error {
+func (e *EmailProvider) Send(ctx context.Context, title, message string) error {
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	default:
+	}
 	auth := smtp.PlainAuth("", e.User, e.Pass, e.Host)
 	msg := []byte("To: " + e.To + "\r\n" +
 		"Subject: Go-Upkeep: " + title + "\r\n" +
@@ -187,9 +198,9 @@ type NtfyProvider struct {
 	Password  string
 }
 
-func (n *NtfyProvider) Send(title, message string) error {
+func (n *NtfyProvider) Send(ctx context.Context, title, message string) error {
 	url := strings.TrimRight(n.ServerURL, "/") + "/" + n.Topic
-	req, err := http.NewRequest("POST", url, strings.NewReader(message))
+	req, err := http.NewRequestWithContext(ctx, "POST", url, strings.NewReader(message))
 	if err != nil {
 		return err
 	}

internal/alert/alert_test.go

@@ -1,6 +1,7 @@
 package alert
 
 import (
+	"context"
 	"encoding/json"
 	"go-upkeep/internal/models"
 	"net/http"
@@ -17,7 +18,7 @@ func TestHTTPProviderDiscord(t *testing.T) {
 	defer srv.Close()
 
 	p := GetProvider(models.AlertConfig{Type: "discord", Settings: map[string]string{"url": srv.URL}})
-	if err := p.Send("Test Title", "Test Body"); err != nil {
+	if err := p.Send(context.Background(), "Test Title", "Test Body"); err != nil {
 		t.Fatalf("Send: %v", err)
 	}
 
@@ -35,7 +36,7 @@ func TestHTTPProviderSlack(t *testing.T) {
 	defer srv.Close()
 
 	p := GetProvider(models.AlertConfig{Type: "slack", Settings: map[string]string{"url": srv.URL}})
-	if err := p.Send("Alert", "Message"); err != nil {
+	if err := p.Send(context.Background(), "Alert", "Message"); err != nil {
 		t.Fatalf("Send: %v", err)
 	}
 
@@ -53,7 +54,7 @@ func TestHTTPProviderWebhook(t *testing.T) {
 	defer srv.Close()
 
 	p := GetProvider(models.AlertConfig{Type: "webhook", Settings: map[string]string{"url": srv.URL}})
-	if err := p.Send("Title", "Body"); err != nil {
+	if err := p.Send(context.Background(), "Title", "Body"); err != nil {
 		t.Fatalf("Send: %v", err)
 	}
 
@@ -69,7 +70,7 @@ func TestHTTPProviderErrorOnHTTP4xx(t *testing.T) {
 	defer srv.Close()
 
 	p := GetProvider(models.AlertConfig{Type: "discord", Settings: map[string]string{"url": srv.URL}})
-	if err := p.Send("Test", "Test"); err == nil {
+	if err := p.Send(context.Background(), "Test", "Test"); err == nil {
 		t.Fatal("expected error on 403 response")
 	}
 }
@@ -89,7 +90,7 @@ func TestNtfyProvider(t *testing.T) {
 		"url":   srv.URL,
 		"topic": "test",
 	}})
-	if err := p.Send("Alert Title", "Alert Body"); err != nil {
+	if err := p.Send(context.Background(), "Alert Title", "Alert Body"); err != nil {
 		t.Fatalf("Send: %v", err)
 	}
 
@@ -110,7 +111,7 @@ func TestHTTPProviderTelegram(t *testing.T) {
 	defer srv.Close()
 
 	p := &HTTPProvider{URL: srv.URL, Payload: telegramPayload("12345")}
-	if err := p.Send("Alert", "Down"); err != nil {
+	if err := p.Send(context.Background(), "Alert", "Down"); err != nil {
 		t.Fatalf("Send: %v", err)
 	}
 	if received["chat_id"] != "12345" {
@@ -133,7 +134,7 @@ func TestHTTPProviderPagerDuty(t *testing.T) {
 	defer srv.Close()
 
 	p := &HTTPProvider{URL: srv.URL, Payload: pagerdutyPayload("test-key", "critical")}
-	if err := p.Send("Alert", "Down"); err != nil {
+	if err := p.Send(context.Background(), "Alert", "Down"); err != nil {
 		t.Fatalf("Send: %v", err)
 	}
 	if received["routing_key"] != "test-key" {
@@ -160,7 +161,7 @@ func TestHTTPProviderPushover(t *testing.T) {
 	defer srv.Close()
 
 	p := &HTTPProvider{URL: srv.URL, Payload: pushoverPayload("app-tok", "user-key")}
-	if err := p.Send("Alert", "Down"); err != nil {
+	if err := p.Send(context.Background(), "Alert", "Down"); err != nil {
 		t.Fatalf("Send: %v", err)
 	}
 	if received["token"] != "app-tok" {
@@ -183,7 +184,7 @@ func TestHTTPProviderGotify(t *testing.T) {
 	defer srv.Close()
 
 	p := &HTTPProvider{URL: srv.URL, Payload: gotifyPayload("8")}
-	if err := p.Send("Alert", "Down"); err != nil {
+	if err := p.Send(context.Background(), "Alert", "Down"); err != nil {
 		t.Fatalf("Send: %v", err)
 	}
 	if received["title"] != "Alert" || received["message"] != "Down" {

internal/cluster/cluster.go

@@ -59,7 +59,7 @@ func runFollowerLoop(ctx context.Context, cfg Config, eng *monitor.Engine) {
 
 		if err == nil && resp.StatusCode == 200 {
 			isLeaderHealthy = true
-			resp.Body.Close()
+			_ = resp.Body.Close()
 		}
 
 		if isLeaderHealthy {

internal/cluster/cluster_test.go

@@ -0,0 +1,394 @@
+package cluster
+
+import (
+	"context"
+	"encoding/json"
+	"go-upkeep/internal/models"
+	"go-upkeep/internal/monitor"
+	"net/http"
+	"net/http/httptest"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+// --- Mock Store (minimal, for monitor.NewEngine) ---
+
+type mockStore struct {
+	sites []models.Site
+}
+
+func (m *mockStore) Init() error                                              { return nil }
+func (m *mockStore) GetSites() ([]models.Site, error)                         { return m.sites, nil }
+func (m *mockStore) AddSite(models.Site) error                                { return nil }
+func (m *mockStore) UpdateSite(models.Site) error                             { return nil }
+func (m *mockStore) UpdateSitePaused(int, bool) error                         { return nil }
+func (m *mockStore) DeleteSite(int) error                                     { return nil }
+func (m *mockStore) GetAllAlerts() ([]models.AlertConfig, error)              { return nil, nil }
+func (m *mockStore) GetAlert(int) (models.AlertConfig, error)                 { return models.AlertConfig{}, nil }
+func (m *mockStore) AddAlert(string, string, map[string]string) error         { return nil }
+func (m *mockStore) UpdateAlert(int, string, string, map[string]string) error { return nil }
+func (m *mockStore) DeleteAlert(int) error                                    { return nil }
+func (m *mockStore) GetAllUsers() ([]models.User, error)                      { return nil, nil }
+func (m *mockStore) AddUser(string, string, string) error                     { return nil }
+func (m *mockStore) UpdateUser(int, string, string, string) error             { return nil }
+func (m *mockStore) DeleteUser(int) error                                     { return nil }
+func (m *mockStore) SaveCheck(int, int64, bool) error                         { return nil }
+func (m *mockStore) SaveCheckFromNode(int, string, int64, bool) error         { return nil }
+func (m *mockStore) LoadAllHistory(int) (map[int][]models.CheckRecord, error) { return nil, nil }
+func (m *mockStore) ExportData() (models.Backup, error)                       { return models.Backup{}, nil }
+func (m *mockStore) ImportData(models.Backup) error                           { return nil }
+func (m *mockStore) GetSiteByName(string) (models.Site, error)                { return models.Site{}, nil }
+func (m *mockStore) GetAlertByName(string) (models.AlertConfig, error) {
+	return models.AlertConfig{}, nil
+}
+func (m *mockStore) AddSiteReturningID(models.Site) (int, error) { return 0, nil }
+func (m *mockStore) AddAlertReturningID(string, string, map[string]string) (int, error) {
+	return 0, nil
+}
+func (m *mockStore) RegisterNode(models.ProbeNode) error      { return nil }
+func (m *mockStore) GetNode(string) (models.ProbeNode, error) { return models.ProbeNode{}, nil }
+func (m *mockStore) GetAllNodes() ([]models.ProbeNode, error) { return nil, nil }
+func (m *mockStore) UpdateNodeLastSeen(string) error          { return nil }
+func (m *mockStore) DeleteNode(string) error                  { return nil }
+func (m *mockStore) SaveLog(string) error                     { return nil }
+func (m *mockStore) LoadLogs(int) ([]string, error)           { return nil, nil }
+func (m *mockStore) GetActiveMaintenanceWindows() ([]models.MaintenanceWindow, error) {
+	return nil, nil
+}
+func (m *mockStore) GetAllMaintenanceWindows(int) ([]models.MaintenanceWindow, error) {
+	return nil, nil
+}
+func (m *mockStore) AddMaintenanceWindow(models.MaintenanceWindow) error { return nil }
+func (m *mockStore) EndMaintenanceWindow(int) error                      { return nil }
+func (m *mockStore) DeleteMaintenanceWindow(int) error                   { return nil }
+func (m *mockStore) IsMonitorInMaintenance(int) (bool, error)            { return false, nil }
+func (m *mockStore) GetPreference(string) (string, error)                { return "", nil }
+func (m *mockStore) SetPreference(string, string) error                  { return nil }
+func (m *mockStore) Close() error                                        { return nil }
+
+// --- Cluster Start Tests ---
+
+func TestStart_LeaderMode(t *testing.T) {
+	eng := monitor.NewEngine(&mockStore{})
+	eng.SetActive(false)
+
+	ctx := context.Background()
+	Start(ctx, Config{Mode: "leader"}, eng)
+
+	if !eng.IsActive() {
+		t.Error("leader mode should set engine active")
+	}
+}
+
+func TestStart_FollowerMode(t *testing.T) {
+	eng := monitor.NewEngine(&mockStore{})
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	Start(ctx, Config{Mode: "follower", PeerURL: "http://localhost:9999"}, eng)
+	time.Sleep(50 * time.Millisecond)
+
+	if eng.IsActive() {
+		t.Error("follower mode should set engine inactive")
+	}
+}
+
+// --- Follower Loop Tests ---
+
+func TestFollowerLoop_FailoverOnLeaderDown(t *testing.T) {
+	eng := monitor.NewEngine(&mockStore{})
+	eng.SetActive(false)
+
+	// Server always returns 503
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(503)
+	}))
+	defer srv.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	go runFollowerLoop(ctx, Config{PeerURL: srv.URL, SharedKey: "key"}, eng)
+
+	// Follower checks every 5s, needs 3 failures → ~15s minimum
+	// But we can't wait that long in a test. The loop sleeps 5s between checks.
+	// We'll wait up to 20s for failover.
+	deadline := time.After(20 * time.Second)
+	for {
+		if eng.IsActive() {
+			return // success
+		}
+		select {
+		case <-deadline:
+			t.Fatal("expected failover to ACTIVE after 3 failures")
+		case <-time.After(500 * time.Millisecond):
+		}
+	}
+}
+
+func TestFollowerLoop_RecoveryOnLeaderReturn(t *testing.T) {
+	eng := monitor.NewEngine(&mockStore{})
+	eng.SetActive(true) // simulate already failed over
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("OK"))
+	}))
+	defer srv.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	go runFollowerLoop(ctx, Config{PeerURL: srv.URL}, eng)
+
+	deadline := time.After(10 * time.Second)
+	for {
+		if !eng.IsActive() {
+			return // success — switched back to passive
+		}
+		select {
+		case <-deadline:
+			t.Fatal("expected switch back to PASSIVE when leader returns")
+		case <-time.After(500 * time.Millisecond):
+		}
+	}
+}
+
+func TestFollowerLoop_SendsSecret(t *testing.T) {
+	var mu sync.Mutex
+	var receivedSecret string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		mu.Lock()
+		receivedSecret = r.Header.Get("X-Upkeep-Secret")
+		mu.Unlock()
+		w.WriteHeader(200)
+		w.Write([]byte("OK"))
+	}))
+	defer srv.Close()
+
+	eng := monitor.NewEngine(&mockStore{})
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	go runFollowerLoop(ctx, Config{PeerURL: srv.URL, SharedKey: "test-secret"}, eng)
+
+	deadline := time.After(10 * time.Second)
+	for {
+		mu.Lock()
+		got := receivedSecret
+		mu.Unlock()
+		if got == "test-secret" {
+			return
+		}
+		select {
+		case <-deadline:
+			t.Fatalf("expected secret 'test-secret', got %q", got)
+		case <-time.After(500 * time.Millisecond):
+		}
+	}
+}
+
+func TestFollowerLoop_CancelContext(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+	}))
+	defer srv.Close()
+
+	eng := monitor.NewEngine(&mockStore{})
+	ctx, cancel := context.WithCancel(context.Background())
+
+	done := make(chan struct{})
+	go func() {
+		runFollowerLoop(ctx, Config{PeerURL: srv.URL}, eng)
+		close(done)
+	}()
+
+	cancel()
+	select {
+	case <-done:
+	case <-time.After(3 * time.Second):
+		t.Fatal("expected follower loop to exit on context cancel")
+	}
+}
+
+// --- Probe Tests ---
+
+func TestProbeRegister_Success(t *testing.T) {
+	var received map[string]string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewDecoder(r.Body).Decode(&received)
+		w.WriteHeader(200)
+	}))
+	defer srv.Close()
+
+	err := probeRegister(context.Background(), srv.Client(), ProbeConfig{
+		NodeID: "n1", NodeName: "US East", Region: "us-east", LeaderURL: srv.URL, SharedKey: "key",
+	})
+	if err != nil {
+		t.Fatalf("register: %v", err)
+	}
+	if received["id"] != "n1" {
+		t.Errorf("expected id n1, got %s", received["id"])
+	}
+}
+
+func TestProbeRegister_Failure(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(401)
+	}))
+	defer srv.Close()
+
+	err := probeRegister(context.Background(), srv.Client(), ProbeConfig{
+		LeaderURL: srv.URL,
+	})
+	if err == nil {
+		t.Error("expected error on 401")
+	}
+}
+
+func TestProbeFetchAssignments_Success(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string][]models.Site{
+			"sites": {{ID: 1, Name: "s1", Type: "http", URL: "http://example.com"}},
+		})
+	}))
+	defer srv.Close()
+
+	sites, err := probeFetchAssignments(context.Background(), srv.Client(), ProbeConfig{
+		NodeID: "n1", LeaderURL: srv.URL, SharedKey: "key",
+	})
+	if err != nil {
+		t.Fatalf("fetch: %v", err)
+	}
+	if len(sites) != 1 {
+		t.Errorf("expected 1 site, got %d", len(sites))
+	}
+}
+
+func TestProbeFetchAssignments_Unauthorized(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(401)
+	}))
+	defer srv.Close()
+
+	_, err := probeFetchAssignments(context.Background(), srv.Client(), ProbeConfig{
+		LeaderURL: srv.URL,
+	})
+	if err == nil {
+		t.Error("expected error on 401")
+	}
+}
+
+func TestProbeExecuteChecks(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+	}))
+	defer srv.Close()
+
+	sites := []models.Site{
+		{ID: 1, Type: "http", URL: srv.URL},
+		{ID: 2, Type: "http", URL: srv.URL},
+	}
+
+	strict := &http.Client{}
+	insecure := &http.Client{}
+	results := probeExecuteChecks(context.Background(), sites, strict, insecure)
+
+	if len(results) != 2 {
+		t.Fatalf("expected 2 results, got %d", len(results))
+	}
+	for _, r := range results {
+		if !r.IsUp {
+			t.Errorf("site %d expected UP", r.SiteID)
+		}
+	}
+}
+
+func TestProbeExecuteChecks_Concurrency(t *testing.T) {
+	var concurrent int64
+	var maxConcurrent int64
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		cur := atomic.AddInt64(&concurrent, 1)
+		for {
+			old := atomic.LoadInt64(&maxConcurrent)
+			if cur <= old || atomic.CompareAndSwapInt64(&maxConcurrent, old, cur) {
+				break
+			}
+		}
+		time.Sleep(50 * time.Millisecond)
+		atomic.AddInt64(&concurrent, -1)
+		w.WriteHeader(200)
+	}))
+	defer srv.Close()
+
+	var sites []models.Site
+	for i := 0; i < 20; i++ {
+		sites = append(sites, models.Site{ID: i + 1, Type: "http", URL: srv.URL})
+	}
+
+	results := probeExecuteChecks(context.Background(), sites, &http.Client{}, &http.Client{})
+	if len(results) != 20 {
+		t.Errorf("expected 20 results, got %d", len(results))
+	}
+	mc := atomic.LoadInt64(&maxConcurrent)
+	if mc > 10 {
+		t.Errorf("expected max 10 concurrent, got %d", mc)
+	}
+}
+
+func TestProbeReportResults_Success(t *testing.T) {
+	var received struct {
+		NodeID  string            `json:"node_id"`
+		Results []probeResultItem `json:"results"`
+	}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewDecoder(r.Body).Decode(&received)
+		w.WriteHeader(200)
+	}))
+	defer srv.Close()
+
+	err := probeReportResults(context.Background(), srv.Client(), ProbeConfig{
+		NodeID: "n1", LeaderURL: srv.URL, SharedKey: "key",
+	}, []probeResultItem{{SiteID: 1, LatencyNs: 5000000, IsUp: true}})
+
+	if err != nil {
+		t.Fatalf("report: %v", err)
+	}
+	if received.NodeID != "n1" {
+		t.Errorf("expected n1, got %s", received.NodeID)
+	}
+	if len(received.Results) != 1 {
+		t.Errorf("expected 1 result, got %d", len(received.Results))
+	}
+}
+
+func TestProbeReportResults_Failure(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(500)
+	}))
+	defer srv.Close()
+
+	err := probeReportResults(context.Background(), srv.Client(), ProbeConfig{
+		LeaderURL: srv.URL,
+	}, []probeResultItem{{SiteID: 1}})
+
+	if err == nil {
+		t.Error("expected error on 500")
+	}
+}
+
+// --- sleepCtx ---
+
+func TestSleepCtx_Cancel(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	start := time.Now()
+	sleepCtx(ctx, 10*time.Second)
+	if time.Since(start) > time.Second {
+		t.Error("expected immediate return on canceled context")
+	}
+}

internal/cluster/probe.go

@@ -33,7 +33,7 @@ func RunProbe(ctx context.Context, cfg ProbeConfig) error {
 		Transport: &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: false}},
 	}
 	insecureClient := &http.Client{
-		Transport: &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: true}},
+		Transport: &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: true}}, //nolint:gosec // intentional for IgnoreTLS sites
 	}
 
 	if err := probeRegister(ctx, apiClient, cfg); err != nil {
@@ -85,7 +85,7 @@ func probeRegister(ctx context.Context, client *http.Client, cfg ProbeConfig) er
 	if err != nil {
 		return err
 	}
-	resp.Body.Close()
+	_ = resp.Body.Close()
 	if resp.StatusCode != 200 {
 		return fmt.Errorf("register returned %d", resp.StatusCode)
 	}
@@ -127,10 +127,11 @@ func probeExecuteChecks(ctx context.Context, sites []models.Site, strict, insecu
 	sem := make(chan struct{}, 10)
 	var wg sync.WaitGroup
 
+loop:
 	for _, site := range sites {
 		select {
 		case <-ctx.Done():
-			break
+			break loop
 		default:
 		}
 		wg.Add(1)
@@ -171,7 +172,7 @@ func probeReportResults(ctx context.Context, client *http.Client, cfg ProbeConfi
 	if err != nil {
 		return err
 	}
-	resp.Body.Close()
+	_ = resp.Body.Close()
 	if resp.StatusCode != 200 {
 		return fmt.Errorf("results returned %d", resp.StatusCode)
 	}

internal/config/export.go

@@ -142,7 +142,7 @@ func WriteFile(f *File, path string) error {
 		_, err = os.Stdout.Write(data)
 		return err
 	}
-	return os.WriteFile(path, data, 0644)
+	return os.WriteFile(path, data, 0644) //nolint:gosec // config files should be group-readable
 }
 
 func LoadFile(path string) (*File, error) {

internal/importer/kuma.go

@@ -96,7 +96,9 @@ func convertKumaNotifications(entries []KumaNotifEntry) map[int]models.AlertConf
 	result := make(map[int]models.AlertConfig)
 	for _, entry := range entries {
 		var cfg KumaNotifConfig
-		json.Unmarshal([]byte(entry.Config), &cfg)
+		if err := json.Unmarshal([]byte(entry.Config), &cfg); err != nil {
+			continue
+		}
 
 		alert := models.AlertConfig{
 			ID:       entry.ID,
@@ -175,7 +177,7 @@ func convertKumaMonitor(m KumaMonitor, alertMap map[int]int) models.Site {
 
 	for nidStr := range m.NotificationIDs {
 		var nid int
-		fmt.Sscanf(nidStr, "%d", &nid)
+		_, _ = fmt.Sscanf(nidStr, "%d", &nid) //nolint:errcheck
 		if upkeepID, ok := alertMap[nid]; ok {
 			site.AlertID = upkeepID
 			break

internal/metrics/prometheus.go

@@ -55,6 +55,15 @@ func Handler(eng *monitor.Engine) http.HandlerFunc {
 			writeGauge(&b, "upkeep_monitor_paused", labels(s), float64(val))
 		}
 
+		writeHelp(&b, "upkeep_monitor_maintenance", "gauge", "Whether the monitor is in a maintenance window (1) or not (0).")
+		for _, s := range sites {
+			val := 0
+			if eng.GetDisplayStatus(s) == "MAINT" {
+				val = 1
+			}
+			writeGauge(&b, "upkeep_monitor_maintenance", labels(s), float64(val))
+		}
+
 		writeHelp(&b, "upkeep_monitor_cert_expiry_timestamp_seconds", "gauge", "Unix timestamp when the SSL certificate expires.")
 		for _, s := range sites {
 			if !s.HasSSL || s.CertExpiry.IsZero() {
@@ -88,7 +97,7 @@ func Handler(eng *monitor.Engine) http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "text/plain; version=0.0.4; charset=utf-8")
-		w.Write([]byte(b.String()))
+		_, _ = w.Write([]byte(b.String())) //nolint:errcheck
 	}
 }
 

internal/metrics/prometheus_test.go

@@ -52,6 +52,19 @@ func (m *mockStore) UpdateNodeLastSeen(string) error                  { return n
 func (m *mockStore) DeleteNode(string) error                          { return nil }
 func (m *mockStore) SaveLog(string) error                             { return nil }
 func (m *mockStore) LoadLogs(int) ([]string, error)                   { return nil, nil }
+func (m *mockStore) GetActiveMaintenanceWindows() ([]models.MaintenanceWindow, error) {
+	return nil, nil
+}
+func (m *mockStore) GetAllMaintenanceWindows(int) ([]models.MaintenanceWindow, error) {
+	return nil, nil
+}
+func (m *mockStore) AddMaintenanceWindow(models.MaintenanceWindow) error { return nil }
+func (m *mockStore) EndMaintenanceWindow(int) error                      { return nil }
+func (m *mockStore) DeleteMaintenanceWindow(int) error                   { return nil }
+func (m *mockStore) IsMonitorInMaintenance(int) (bool, error)            { return false, nil }
+func (m *mockStore) GetPreference(string) (string, error)                { return "", nil }
+func (m *mockStore) SetPreference(string, string) error                  { return nil }
+func (m *mockStore) Close() error                                        { return nil }
 
 func TestMetricsHandler(t *testing.T) {
 	ms := &mockStore{

internal/models/models.go

@@ -67,8 +67,21 @@ type ProbeNode struct {
 	Version  string
 }
 
-type Backup struct {
+type MaintenanceWindow struct {
-	Sites  []Site        `json:"sites"`
+	ID          int
-	Alerts []AlertConfig `json:"alerts"`
+	MonitorID   int
-	Users  []User        `json:"users"`
+	Title       string
+	Description string
+	Type        string // "maintenance" or "incident"
+	StartTime   time.Time
+	EndTime     time.Time // zero = ongoing
+	CreatedBy   string
+	CreatedAt   time.Time
+}
+
+type Backup struct {
+	Sites              []Site              `json:"sites"`
+	Alerts             []AlertConfig       `json:"alerts"`
+	Users              []User              `json:"users"`
+	MaintenanceWindows []MaintenanceWindow `json:"maintenance_windows,omitempty"`
 }

internal/monitor/checker.go

@@ -131,7 +131,7 @@ func runPortCheck(site models.Site) CheckResult {
 	if err != nil {
 		return CheckResult{SiteID: site.ID, Status: "DOWN", LatencyNs: latency.Nanoseconds()}
 	}
-	conn.Close()
+	_ = conn.Close()
 	return CheckResult{SiteID: site.ID, Status: "UP", LatencyNs: latency.Nanoseconds()}
 }
 

internal/monitor/checker_test.go

@@ -0,0 +1,203 @@
+package monitor
+
+import (
+	"crypto/tls"
+	"go-upkeep/internal/models"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"testing"
+	"time"
+)
+
+func TestRunCheck_HTTP_Success(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+	}))
+	defer srv.Close()
+
+	site := models.Site{ID: 1, Type: "http", URL: srv.URL}
+	result := RunCheck(site, http.DefaultClient, http.DefaultClient, false)
+
+	if result.Status != "UP" {
+		t.Errorf("expected UP, got %s", result.Status)
+	}
+	if result.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", result.StatusCode)
+	}
+	if result.LatencyNs <= 0 {
+		t.Error("expected positive latency")
+	}
+}
+
+func TestRunCheck_HTTP_ServerError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(500)
+	}))
+	defer srv.Close()
+
+	site := models.Site{ID: 1, Type: "http", URL: srv.URL}
+	result := RunCheck(site, http.DefaultClient, http.DefaultClient, false)
+
+	if result.Status != "DOWN" {
+		t.Errorf("expected DOWN, got %s", result.Status)
+	}
+	if result.StatusCode != 500 {
+		t.Errorf("expected 500, got %d", result.StatusCode)
+	}
+}
+
+func TestRunCheck_HTTP_CustomAcceptedCodes(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(302)
+	}))
+	defer srv.Close()
+
+	client := &http.Client{CheckRedirect: func(req *http.Request, via []*http.Request) error {
+		return http.ErrUseLastResponse
+	}}
+
+	site := models.Site{ID: 1, Type: "http", URL: srv.URL, AcceptedCodes: "200-399"}
+	result := RunCheck(site, client, client, false)
+
+	if result.Status != "UP" {
+		t.Errorf("expected UP with accepted 200-399, got %s", result.Status)
+	}
+}
+
+func TestRunCheck_HTTP_MethodRespected(t *testing.T) {
+	var receivedMethod string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		receivedMethod = r.Method
+		w.WriteHeader(200)
+	}))
+	defer srv.Close()
+
+	site := models.Site{ID: 1, Type: "http", URL: srv.URL, Method: "HEAD"}
+	RunCheck(site, http.DefaultClient, http.DefaultClient, false)
+
+	if receivedMethod != "HEAD" {
+		t.Errorf("expected HEAD, got %s", receivedMethod)
+	}
+}
+
+func TestRunCheck_HTTP_Timeout(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		time.Sleep(2 * time.Second)
+		w.WriteHeader(200)
+	}))
+	defer srv.Close()
+
+	site := models.Site{ID: 1, Type: "http", URL: srv.URL, Timeout: 1}
+	result := RunCheck(site, http.DefaultClient, http.DefaultClient, false)
+
+	if result.Status != "DOWN" {
+		t.Errorf("expected DOWN on timeout, got %s", result.Status)
+	}
+}
+
+func TestRunCheck_HTTP_SSLFields(t *testing.T) {
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+	}))
+	defer srv.Close()
+
+	insecureClient := &http.Client{
+		Transport: &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: true}},
+	}
+
+	site := models.Site{ID: 1, Type: "http", URL: srv.URL, CheckSSL: true, IgnoreTLS: true}
+	result := RunCheck(site, http.DefaultClient, insecureClient, false)
+
+	if result.Status != "UP" {
+		t.Errorf("expected UP, got %s", result.Status)
+	}
+	if !result.HasSSL {
+		t.Error("expected HasSSL=true")
+	}
+	if result.CertExpiry.IsZero() {
+		t.Error("expected CertExpiry populated")
+	}
+}
+
+func TestRunCheck_Port_Open(t *testing.T) {
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+
+	_, portStr, _ := net.SplitHostPort(ln.Addr().String())
+	port, _ := strconv.Atoi(portStr)
+
+	site := models.Site{ID: 1, Type: "port", Hostname: "127.0.0.1", Port: port, Timeout: 2}
+	result := RunCheck(site, nil, nil, false)
+
+	if result.Status != "UP" {
+		t.Errorf("expected UP, got %s", result.Status)
+	}
+	if result.LatencyNs <= 0 {
+		t.Error("expected positive latency")
+	}
+}
+
+func TestRunCheck_Port_Closed(t *testing.T) {
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, portStr, _ := net.SplitHostPort(ln.Addr().String())
+	port, _ := strconv.Atoi(portStr)
+	ln.Close()
+
+	site := models.Site{ID: 1, Type: "port", Hostname: "127.0.0.1", Port: port, Timeout: 1}
+	result := RunCheck(site, nil, nil, false)
+
+	if result.Status != "DOWN" {
+		t.Errorf("expected DOWN, got %s", result.Status)
+	}
+}
+
+func TestRunCheck_UnknownType(t *testing.T) {
+	site := models.Site{ID: 1, Type: "invalid"}
+	result := RunCheck(site, nil, nil, false)
+
+	if result.Status != "DOWN" {
+		t.Errorf("expected DOWN for unknown type, got %s", result.Status)
+	}
+}
+
+func TestIsCodeAccepted(t *testing.T) {
+	tests := []struct {
+		code     int
+		accepted string
+		want     bool
+	}{
+		{200, "", true},
+		{299, "", true},
+		{300, "", false},
+		{302, "200-399", true},
+		{400, "200-399", false},
+		{301, "200,301,404", true},
+		{500, "200,301,404", false},
+		{404, "200-299,400-499", true},
+		{500, "200-299,400-499", false},
+	}
+
+	for _, tt := range tests {
+		got := isCodeAccepted(tt.code, tt.accepted)
+		if got != tt.want {
+			t.Errorf("isCodeAccepted(%d, %q) = %v, want %v", tt.code, tt.accepted, got, tt.want)
+		}
+	}
+}
+
+func TestSiteTimeout(t *testing.T) {
+	if got := siteTimeout(models.Site{Timeout: 0}); got != 5*time.Second {
+		t.Errorf("expected 5s default, got %v", got)
+	}
+	if got := siteTimeout(models.Site{Timeout: 10}); got != 10*time.Second {
+		t.Errorf("expected 10s, got %v", got)
+	}
+}

internal/monitor/monitor.go

@@ -7,6 +7,7 @@ import (
 	"go-upkeep/internal/alert"
 	"go-upkeep/internal/models"
 	"go-upkeep/internal/store"
+	"math/rand/v2"
 	"net/http"
 	"sync"
 	"time"
@@ -25,7 +26,7 @@ type Engine struct {
 	histMu    sync.RWMutex
 	histories map[int]*SiteHistory
 
-	tokenIndex map[string]int
+	tokenIndex map[string]int // protected by mu
 
 	probeResultsMu sync.RWMutex
 	probeResults   map[int]map[string]NodeResult
@@ -50,7 +51,7 @@ func NewEngine(s store.Store) *Engine {
 			Transport: &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: false}},
 		},
 		insecureClient: &http.Client{
-			Transport: &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: true}},
+			Transport: &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: true}}, //nolint:gosec // intentional for IgnoreTLS sites
 		},
 	}
 }
@@ -277,6 +278,14 @@ func (e *Engine) ToggleSitePause(id int) bool {
 }
 
 func (e *Engine) monitorRoutine(ctx context.Context, id int) {
+	// Stagger initial check to avoid thundering herd on startup
+	stagger := time.Duration(rand.IntN(3000)) * time.Millisecond //nolint:gosec // non-security jitter
+	select {
+	case <-time.After(stagger):
+	case <-ctx.Done():
+		return
+	}
+
 	e.checkByID(id)
 	for {
 		select {
@@ -314,8 +323,9 @@ func (e *Engine) monitorRoutine(ctx context.Context, id int) {
 		if interval < 5 {
 			interval = 5
 		}
+		jitter := time.Duration(rand.IntN(interval*100)) * time.Millisecond //nolint:gosec // non-security jitter
 		select {
-		case <-time.After(time.Duration(interval) * time.Second):
+		case <-time.After(time.Duration(interval)*time.Second + jitter):
 		case <-ctx.Done():
 			return
 		}
@@ -385,10 +395,16 @@ func (e *Engine) handleStatusChange(site models.Site, rawStatus string, code int
 		newState.FailureCount = site.MaxRetries + 1
 	}
 
+	inMaint := e.isInMaintenance(site.ID)
+
 	if site.Type == "http" && site.CheckSSL && site.HasSSL {
 		daysLeft := int(time.Until(site.CertExpiry).Hours() / 24)
 		if daysLeft <= site.ExpiryThreshold && !site.SentSSLWarning && rawStatus != "SSL EXP" {
-			e.triggerAlert(site.AlertID, "SSL WARNING", fmt.Sprintf("SSL for '%s' expires in %d days", site.Name, daysLeft))
+			if !inMaint {
+				e.triggerAlert(site.AlertID, "SSL WARNING", fmt.Sprintf("SSL for '%s' expires in %d days", site.Name, daysLeft))
+			} else {
+				e.AddLog(fmt.Sprintf("SSL warning for '%s' suppressed (maintenance)", site.Name))
+			}
 			newState.SentSSLWarning = true
 		} else if daysLeft > site.ExpiryThreshold {
 			newState.SentSSLWarning = false
@@ -405,20 +421,29 @@ func (e *Engine) handleStatusChange(site models.Site, rawStatus string, code int
 
 	isBroken := func(s string) bool { return s == "DOWN" || s == "SSL EXP" }
 	if !isBroken(site.Status) && isBroken(newState.Status) && newState.Status != "PENDING" {
-		msg := fmt.Sprintf("Monitor '%s' is DOWN (%s)", site.Name, rawStatus)
+		if inMaint {
-		if site.Type == "push" {
+			e.AddLog(fmt.Sprintf("Monitor '%s' is DOWN (alerts suppressed — maintenance)", site.Name))
-			msg = fmt.Sprintf("Push Monitor '%s' missed heartbeat.", site.Name)
+		} else {
+			msg := fmt.Sprintf("Monitor '%s' is DOWN (%s)", site.Name, rawStatus)
+			if site.Type == "push" {
+				msg = fmt.Sprintf("Push Monitor '%s' missed heartbeat.", site.Name)
+			}
+			e.triggerAlert(site.AlertID, "🚨 ALERT", msg)
 		}
-		e.triggerAlert(site.AlertID, "🚨 ALERT", msg)
 	}
 	if isBroken(site.Status) && newState.Status == "UP" {
-		e.triggerAlert(site.AlertID, "✅ RECOVERY", fmt.Sprintf("Monitor '%s' is UP", site.Name))
+		if !inMaint {
+			e.triggerAlert(site.AlertID, "✅ RECOVERY", fmt.Sprintf("Monitor '%s' is UP", site.Name))
+		} else {
+			e.AddLog(fmt.Sprintf("Monitor '%s' recovered (maintenance active, alert suppressed)", site.Name))
+		}
 	}
 }
 
 func (e *Engine) triggerAlert(alertID int, title, message string) {
 	cfg, err := e.db.GetAlert(alertID)
 	if err != nil {
+		e.AddLog(fmt.Sprintf("Failed to load alert config %d: %v", alertID, err))
 		return
 	}
 	provider := alert.GetProvider(cfg)
@@ -426,12 +451,31 @@ func (e *Engine) triggerAlert(alertID int, title, message string) {
 		go func() {
 			ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 			defer cancel()
-			_ = ctx
+			if err := provider.Send(ctx, title, message); err != nil {
-			_ = provider.Send(title, message)
+				e.AddLog(fmt.Sprintf("Alert send failed (%s): %v", cfg.Name, err))
+			}
 		}()
 	}
 }
 
+func (e *Engine) isInMaintenance(monitorID int) bool {
+	inMaint, err := e.db.IsMonitorInMaintenance(monitorID)
+	if err != nil {
+		return false
+	}
+	return inMaint
+}
+
+func (e *Engine) GetDisplayStatus(site models.Site) string {
+	if site.Paused {
+		return "PAUSED"
+	}
+	if e.isInMaintenance(site.ID) {
+		return "MAINT"
+	}
+	return site.Status
+}
+
 func (e *Engine) checkGroup(site models.Site) {
 	e.mu.RLock()
 	status := "UP"
@@ -445,7 +489,7 @@ func (e *Engine) checkGroup(site models.Site) {
 		if !child.Paused {
 			allPaused = false
 		}
-		if child.Paused {
+		if child.Paused || e.isInMaintenance(child.ID) {
 			continue
 		}
 		if child.Status == "DOWN" || child.Status == "SSL EXP" {

internal/server/server.go

@@ -1,6 +1,7 @@
 package server
 
 import (
+	"crypto/subtle"
 	"encoding/json"
 	"fmt"
 	"go-upkeep/internal/importer"
@@ -13,8 +14,13 @@ import (
 	"net/http"
 	"sort"
 	"strings"
+	"time"
 )
 
+func checkSecret(got, want string) bool {
+	return subtle.ConstantTimeCompare([]byte(got), []byte(want)) == 1
+}
+
 var statusTpl = template.Must(template.New("status").Parse(`
 <!DOCTYPE html>
 <html>
@@ -35,6 +41,7 @@ var statusTpl = template.Must(template.New("status").Parse(`
 		.PENDING { background: #e0af68; color: #1a1b26; }
 		.SSL-EXP { background: #e0af68; color: #1a1b26; }
 		.PAUSED { background: #565f89; color: #c0caf5; }
+		.MAINT { background: #bb9af7; color: #1a1b26; }
 		.summary { display: flex; justify-content: center; gap: 16px; margin-bottom: 24px; font-size: 0.95em; font-weight: 600; }
 		.summary span { padding: 4px 12px; border-radius: 6px; }
 		.summary .s-up { color: #9ece6a; }
@@ -68,15 +75,17 @@ var statusTpl = template.Must(template.New("status").Parse(`
 		}
 
 		function renderSummary(sites) {
-			var up = 0, down = 0, paused = 0, total = sites.length;
+			var up = 0, down = 0, paused = 0, maint = 0, total = sites.length;
 			for (var i = 0; i < sites.length; i++) {
 				if (sites[i].Paused) { paused++; continue; }
+				if (sites[i].Status === 'MAINT') { maint++; continue; }
 				if (sites[i].Status === 'UP') up++;
 				else if (sites[i].Status === 'DOWN') down++;
 			}
 			var el = document.getElementById('summary');
 			var parts = ['<span class="s-total">' + up + '/' + total + ' UP</span>'];
 			if (down > 0) parts.push('<span class="s-down">' + down + ' DOWN</span>');
+			if (maint > 0) parts.push('<span style="color:#bb9af7">' + maint + ' MAINT</span>');
 			if (paused > 0) parts.push('<span class="s-paused">' + paused + ' PAUSED</span>');
 			el.innerHTML = parts.join('<span style="color:#383838">·</span>');
 		}
@@ -110,7 +119,7 @@ var statusTpl = template.Must(template.New("status").Parse(`
 			renderSummary(sites);
 			for (var i = 0; i < sites.length; i++) {
 				var s = sites[i];
-				var st = s.Paused ? 'PAUSED' : s.Status;
+				var st = s.Status === 'MAINT' ? 'MAINT' : s.Paused ? 'PAUSED' : s.Status;
 				var cls = cssClass(st);
 				var meta = esc(s.Type) + ' | ' + (s.Type === 'http' ? esc(s.URL) : 'Heartbeat Monitor');
 				var lc = s.LastCheck ? new Date(s.LastCheck).toLocaleTimeString('en-GB', {hour12: false}) : '—';
@@ -150,7 +159,7 @@ type ServerConfig struct {
 	ClusterKey   string // Shared Secret for Security
 }
 
-func Start(cfg ServerConfig, s store.Store, eng *monitor.Engine) {
+func Start(cfg ServerConfig, s store.Store, eng *monitor.Engine) *http.Server {
 	if cfg.ClusterKey == "" {
 		fmt.Println("WARNING: No UPKEEP_CLUSTER_SECRET set. Cluster API endpoints are unauthenticated.")
 	}
@@ -160,100 +169,103 @@ func Start(cfg ServerConfig, s store.Store, eng *monitor.Engine) {
 	mux.HandleFunc("/api/push", func(w http.ResponseWriter, r *http.Request) {
 		token := r.URL.Query().Get("token")
 		if token == "" {
-			http.Error(w, "Missing token", 400)
+			http.Error(w, "Missing token", http.StatusBadRequest)
 			return
 		}
 		if eng.RecordHeartbeat(token) {
 			w.WriteHeader(http.StatusOK)
-			w.Write([]byte("OK"))
+			_, _ = w.Write([]byte("OK"))
 		} else {
-			http.Error(w, "Invalid Token", 404)
+			http.Error(w, "Invalid Token", http.StatusNotFound)
 		}
 	})
 
 	// 2. Health Check (For Cluster Follower)
 	mux.HandleFunc("/api/health", func(w http.ResponseWriter, r *http.Request) {
-		if cfg.ClusterKey != "" && r.Header.Get("X-Upkeep-Secret") != cfg.ClusterKey {
+		if cfg.ClusterKey != "" && !checkSecret(r.Header.Get("X-Upkeep-Secret"), cfg.ClusterKey) {
-			http.Error(w, "Unauthorized", 401)
+			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 			return
 		}
 		w.WriteHeader(http.StatusOK)
-		w.Write([]byte("OK"))
+		_, _ = w.Write([]byte("OK"))
 	})
 
 	// 3. Config Export
 	mux.HandleFunc("/api/backup/export", func(w http.ResponseWriter, r *http.Request) {
-		if cfg.ClusterKey == "" || r.Header.Get("X-Upkeep-Secret") != cfg.ClusterKey {
+		if cfg.ClusterKey == "" || !checkSecret(r.Header.Get("X-Upkeep-Secret"), cfg.ClusterKey) {
-			http.Error(w, "Unauthorized: UPKEEP_CLUSTER_SECRET required", 401)
+			http.Error(w, "Unauthorized: UPKEEP_CLUSTER_SECRET required", http.StatusUnauthorized)
 			return
 		}
 		data, err := s.ExportData()
 		if err != nil {
 			log.Printf("Export failed: %v", err)
-			http.Error(w, "Export failed", 500)
+			http.Error(w, "Export failed", http.StatusInternalServerError)
 			return
 		}
-		json.NewEncoder(w).Encode(data)
+		_ = json.NewEncoder(w).Encode(data) //nolint:errcheck
 	})
 
 	// 4. Config Import
 	mux.HandleFunc("/api/backup/import", func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != "POST" {
-			http.Error(w, "POST required", 405)
+			http.Error(w, "POST required", http.StatusMethodNotAllowed)
 			return
 		}
-		if cfg.ClusterKey == "" || r.Header.Get("X-Upkeep-Secret") != cfg.ClusterKey {
+		if cfg.ClusterKey == "" || !checkSecret(r.Header.Get("X-Upkeep-Secret"), cfg.ClusterKey) {
-			http.Error(w, "Unauthorized", 401)
+			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 			return
 		}
+		r.Body = http.MaxBytesReader(w, r.Body, 1<<20)
 		var data models.Backup
 		if err := json.NewDecoder(r.Body).Decode(&data); err != nil {
-			http.Error(w, "Invalid JSON", 400)
+			http.Error(w, "Invalid JSON", http.StatusBadRequest)
 			return
 		}
 		if err := s.ImportData(data); err != nil {
 			log.Printf("Import failed: %v", err)
-			http.Error(w, "Import failed", 500)
+			http.Error(w, "Import failed", http.StatusInternalServerError)
 			return
 		}
-		w.Write([]byte("Import Successful"))
+		_, _ = w.Write([]byte("Import Successful"))
 	})
 
 	// 5. Kuma Import
 	mux.HandleFunc("/api/import/kuma", func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != "POST" {
-			http.Error(w, "POST required", 405)
+			http.Error(w, "POST required", http.StatusMethodNotAllowed)
 			return
 		}
-		if cfg.ClusterKey == "" || r.Header.Get("X-Upkeep-Secret") != cfg.ClusterKey {
+		if cfg.ClusterKey == "" || !checkSecret(r.Header.Get("X-Upkeep-Secret"), cfg.ClusterKey) {
-			http.Error(w, "Unauthorized", 401)
+			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 			return
 		}
+		r.Body = http.MaxBytesReader(w, r.Body, 1<<20)
 		var kb importer.KumaBackup
 		if err := json.NewDecoder(r.Body).Decode(&kb); err != nil {
 			log.Printf("Invalid Kuma JSON: %v", err)
-			http.Error(w, "Invalid Kuma JSON", 400)
+			http.Error(w, "Invalid Kuma JSON", http.StatusBadRequest)
 			return
 		}
 		backup := importer.ConvertKuma(&kb)
 		if err := s.ImportData(backup); err != nil {
 			log.Printf("Kuma import failed: %v", err)
-			http.Error(w, "Import failed", 500)
+			http.Error(w, "Import failed", http.StatusInternalServerError)
 			return
 		}
-		w.Write([]byte(fmt.Sprintf("Imported %d monitors, %d alerts from Kuma v%s", len(backup.Sites), len(backup.Alerts), kb.Version)))
+		fmt.Fprintf(w, "Imported %d monitors, %d alerts from Kuma v%s", len(backup.Sites), len(backup.Alerts), kb.Version)
 	})
 
 	// 6. Probe Registration
 	mux.HandleFunc("/api/probe/register", func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != "POST" {
-			http.Error(w, "POST required", 405)
+			http.Error(w, "POST required", http.StatusMethodNotAllowed)
 			return
 		}
-		if cfg.ClusterKey == "" || r.Header.Get("X-Upkeep-Secret") != cfg.ClusterKey {
+		if cfg.ClusterKey == "" || !checkSecret(r.Header.Get("X-Upkeep-Secret"), cfg.ClusterKey) {
-			http.Error(w, "Unauthorized", 401)
+			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 			return
 		}
+		r.Body = http.MaxBytesReader(w, r.Body, 1<<20)
 		var req struct {
 			ID      string `json:"id"`
 			Name    string `json:"name"`
@@ -261,27 +273,27 @@ func Start(cfg ServerConfig, s store.Store, eng *monitor.Engine) {
 			Version string `json:"version"`
 		}
 		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-			http.Error(w, "Invalid JSON", 400)
+			http.Error(w, "Invalid JSON", http.StatusBadRequest)
 			return
 		}
 		if req.ID == "" {
-			http.Error(w, "id is required", 400)
+			http.Error(w, "id is required", http.StatusBadRequest)
 			return
 		}
 		if err := s.RegisterNode(models.ProbeNode{
 			ID: req.ID, Name: req.Name, Region: req.Region, Version: req.Version,
 		}); err != nil {
 			log.Printf("Probe register failed: %v", err)
-			http.Error(w, "Registration failed", 500)
+			http.Error(w, "Registration failed", http.StatusInternalServerError)
 			return
 		}
-		json.NewEncoder(w).Encode(map[string]bool{"ok": true})
+		_ = json.NewEncoder(w).Encode(map[string]bool{"ok": true}) //nolint:errcheck
 	})
 
 	// 7. Probe Assignment Fetch
 	mux.HandleFunc("/api/probe/assignments", func(w http.ResponseWriter, r *http.Request) {
-		if cfg.ClusterKey == "" || r.Header.Get("X-Upkeep-Secret") != cfg.ClusterKey {
+		if cfg.ClusterKey == "" || !checkSecret(r.Header.Get("X-Upkeep-Secret"), cfg.ClusterKey) {
-			http.Error(w, "Unauthorized", 401)
+			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 			return
 		}
 		nodeID := r.URL.Query().Get("node_id")
@@ -312,19 +324,20 @@ func Start(cfg ServerConfig, s store.Store, eng *monitor.Engine) {
 			assigned = append(assigned, site)
 		}
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string][]models.Site{"sites": assigned})
+		_ = json.NewEncoder(w).Encode(map[string][]models.Site{"sites": assigned}) //nolint:errcheck
 	})
 
 	// 8. Probe Result Submission
 	mux.HandleFunc("/api/probe/results", func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != "POST" {
-			http.Error(w, "POST required", 405)
+			http.Error(w, "POST required", http.StatusMethodNotAllowed)
 			return
 		}
-		if cfg.ClusterKey == "" || r.Header.Get("X-Upkeep-Secret") != cfg.ClusterKey {
+		if cfg.ClusterKey == "" || !checkSecret(r.Header.Get("X-Upkeep-Secret"), cfg.ClusterKey) {
-			http.Error(w, "Unauthorized", 401)
+			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 			return
 		}
+		r.Body = http.MaxBytesReader(w, r.Body, 1<<20)
 		var req struct {
 			NodeID  string `json:"node_id"`
 			Results []struct {
@@ -334,11 +347,11 @@ func Start(cfg ServerConfig, s store.Store, eng *monitor.Engine) {
 			} `json:"results"`
 		}
 		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-			http.Error(w, "Invalid JSON", 400)
+			http.Error(w, "Invalid JSON", http.StatusBadRequest)
 			return
 		}
 		if req.NodeID == "" {
-			http.Error(w, "node_id is required", 400)
+			http.Error(w, "node_id is required", http.StatusBadRequest)
 			return
 		}
 		for _, result := range req.Results {
@@ -347,8 +360,10 @@ func Start(cfg ServerConfig, s store.Store, eng *monitor.Engine) {
 			}
 			eng.IngestProbeResult(req.NodeID, result.SiteID, result.LatencyNs, result.IsUp)
 		}
-		s.UpdateNodeLastSeen(req.NodeID)
+		if err := s.UpdateNodeLastSeen(req.NodeID); err != nil {
-		json.NewEncoder(w).Encode(map[string]bool{"ok": true})
+			log.Printf("Failed to update node last seen: %v", err)
+		}
+		_ = json.NewEncoder(w).Encode(map[string]bool{"ok": true}) //nolint:errcheck
 	})
 
 	// 9. Prometheus Metrics
@@ -359,22 +374,40 @@ func Start(cfg ServerConfig, s store.Store, eng *monitor.Engine) {
 		mux.HandleFunc("/status", func(w http.ResponseWriter, r *http.Request) { renderStatusPage(w, cfg.Title, eng) })
 		mux.HandleFunc("/status/json", func(w http.ResponseWriter, r *http.Request) {
 			state := eng.GetLiveState()
+			activeWindows, _ := s.GetActiveMaintenanceWindows()
+			maintSet := make(map[int]bool)
+			allInMaint := false
+			for _, mw := range activeWindows {
+				if mw.Type != "maintenance" {
+					continue
+				}
+				if mw.MonitorID == 0 {
+					allInMaint = true
+				} else {
+					maintSet[mw.MonitorID] = true
+				}
+			}
 			for id, site := range state {
 				site.Token = ""
+				if allInMaint || maintSet[site.ID] || (site.ParentID > 0 && maintSet[site.ParentID]) {
+					site.Status = "MAINT"
+				}
 				state[id] = site
 			}
 			w.Header().Set("Content-Type", "application/json")
-			json.NewEncoder(w).Encode(state)
+			_ = json.NewEncoder(w).Encode(state) //nolint:errcheck
 		})
 	}
 
+	addr := fmt.Sprintf(":%d", cfg.Port)
+	srv := &http.Server{Addr: addr, Handler: mux, ReadHeaderTimeout: 10 * time.Second}
 	go func() {
-		addr := fmt.Sprintf(":%d", cfg.Port)
 		fmt.Printf("HTTP Server listening on %s\n", addr)
-		if err := http.ListenAndServe(addr, mux); err != nil {
+		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
-			log.Fatalf("HTTP server failed: %v", err)
+			log.Printf("HTTP server error: %v", err)
 		}
 	}()
+	return srv
 }
 
 func renderStatusPage(w http.ResponseWriter, title string, eng *monitor.Engine) {
@@ -396,5 +429,7 @@ func renderStatusPage(w http.ResponseWriter, title string, eng *monitor.Engine)
 		Title string
 		Sites []models.Site
 	}{Title: title, Sites: sites}
-	statusTpl.Execute(w, data)
+	if err := statusTpl.Execute(w, data); err != nil {
+		log.Printf("Failed to render status page: %v", err)
+	}
 }

internal/server/server_test.go

@@ -0,0 +1,553 @@
+package server
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"go-upkeep/internal/models"
+	"go-upkeep/internal/monitor"
+	"net"
+	"net/http"
+	"sync"
+	"testing"
+	"time"
+)
+
+// --- Mock Store ---
+
+type mockStore struct {
+	mu              sync.Mutex
+	sites           []models.Site
+	alerts          []models.AlertConfig
+	nodes           map[string]models.ProbeNode
+	importedData    *models.Backup
+	registeredNodes []models.ProbeNode
+	maintWindows    []models.MaintenanceWindow
+}
+
+func newMockStore() *mockStore {
+	return &mockStore{
+		nodes: make(map[string]models.ProbeNode),
+	}
+}
+
+func (m *mockStore) Init() error                                              { return nil }
+func (m *mockStore) GetSites() ([]models.Site, error)                         { return m.sites, nil }
+func (m *mockStore) AddSite(models.Site) error                                { return nil }
+func (m *mockStore) UpdateSite(models.Site) error                             { return nil }
+func (m *mockStore) UpdateSitePaused(int, bool) error                         { return nil }
+func (m *mockStore) DeleteSite(int) error                                     { return nil }
+func (m *mockStore) GetAllAlerts() ([]models.AlertConfig, error)              { return m.alerts, nil }
+func (m *mockStore) GetAlert(int) (models.AlertConfig, error)                 { return models.AlertConfig{}, nil }
+func (m *mockStore) AddAlert(string, string, map[string]string) error         { return nil }
+func (m *mockStore) UpdateAlert(int, string, string, map[string]string) error { return nil }
+func (m *mockStore) DeleteAlert(int) error                                    { return nil }
+func (m *mockStore) GetAllUsers() ([]models.User, error)                      { return nil, nil }
+func (m *mockStore) AddUser(string, string, string) error                     { return nil }
+func (m *mockStore) UpdateUser(int, string, string, string) error             { return nil }
+func (m *mockStore) DeleteUser(int) error                                     { return nil }
+func (m *mockStore) SaveCheck(int, int64, bool) error                         { return nil }
+func (m *mockStore) SaveCheckFromNode(siteID int, nodeID string, latencyNs int64, isUp bool) error {
+	return nil
+}
+func (m *mockStore) LoadAllHistory(int) (map[int][]models.CheckRecord, error) {
+	return nil, nil
+}
+func (m *mockStore) GetSiteByName(string) (models.Site, error) { return models.Site{}, nil }
+func (m *mockStore) GetAlertByName(string) (models.AlertConfig, error) {
+	return models.AlertConfig{}, nil
+}
+func (m *mockStore) AddSiteReturningID(models.Site) (int, error) { return 0, nil }
+func (m *mockStore) AddAlertReturningID(string, string, map[string]string) (int, error) {
+	return 0, nil
+}
+func (m *mockStore) GetAllNodes() ([]models.ProbeNode, error) { return nil, nil }
+func (m *mockStore) UpdateNodeLastSeen(string) error          { return nil }
+func (m *mockStore) DeleteNode(string) error                  { return nil }
+func (m *mockStore) SaveLog(string) error                     { return nil }
+func (m *mockStore) LoadLogs(int) ([]string, error)           { return nil, nil }
+func (m *mockStore) GetAllMaintenanceWindows(int) ([]models.MaintenanceWindow, error) {
+	return nil, nil
+}
+func (m *mockStore) AddMaintenanceWindow(models.MaintenanceWindow) error { return nil }
+func (m *mockStore) EndMaintenanceWindow(int) error                      { return nil }
+func (m *mockStore) DeleteMaintenanceWindow(int) error                   { return nil }
+func (m *mockStore) IsMonitorInMaintenance(int) (bool, error)            { return false, nil }
+func (m *mockStore) GetPreference(string) (string, error)                { return "", nil }
+func (m *mockStore) SetPreference(string, string) error                  { return nil }
+func (m *mockStore) Close() error                                        { return nil }
+
+func (m *mockStore) ExportData() (models.Backup, error) {
+	return models.Backup{
+		Sites:  m.sites,
+		Alerts: m.alerts,
+	}, nil
+}
+
+func (m *mockStore) ImportData(data models.Backup) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.importedData = &data
+	return nil
+}
+
+func (m *mockStore) RegisterNode(node models.ProbeNode) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.registeredNodes = append(m.registeredNodes, node)
+	m.nodes[node.ID] = node
+	return nil
+}
+
+func (m *mockStore) GetNode(id string) (models.ProbeNode, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if n, ok := m.nodes[id]; ok {
+		return n, nil
+	}
+	return models.ProbeNode{}, fmt.Errorf("not found")
+}
+
+func (m *mockStore) GetActiveMaintenanceWindows() ([]models.MaintenanceWindow, error) {
+	return m.maintWindows, nil
+}
+
+// --- Helpers ---
+
+func freePort() int {
+	ln, _ := net.Listen("tcp", "127.0.0.1:0")
+	port := ln.Addr().(*net.TCPAddr).Port
+	ln.Close()
+	return port
+}
+
+type testServer struct {
+	baseURL string
+	srv     *http.Server
+	store   *mockStore
+	engine  *monitor.Engine
+}
+
+func newTestServer(t *testing.T, clusterKey string, enableStatus bool) *testServer {
+	t.Helper()
+	ms := newMockStore()
+	eng := monitor.NewEngine(ms)
+	port := freePort()
+
+	srv := Start(ServerConfig{
+		Port:         port,
+		EnableStatus: enableStatus,
+		Title:        "Test Status",
+		ClusterKey:   clusterKey,
+	}, ms, eng)
+
+	ts := &testServer{
+		baseURL: fmt.Sprintf("http://127.0.0.1:%d", port),
+		srv:     srv,
+		store:   ms,
+		engine:  eng,
+	}
+
+	// Wait for server to be ready
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		resp, err := http.Get(ts.baseURL + "/api/health")
+		if err == nil {
+			resp.Body.Close()
+			break
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	t.Cleanup(func() {
+		srv.Close()
+	})
+
+	return ts
+}
+
+func authReq(method, url, secret string, body []byte) (*http.Response, error) {
+	var req *http.Request
+	var err error
+	if body != nil {
+		req, err = http.NewRequest(method, url, bytes.NewReader(body))
+	} else {
+		req, err = http.NewRequest(method, url, nil)
+	}
+	if err != nil {
+		return nil, err
+	}
+	if secret != "" {
+		req.Header.Set("X-Upkeep-Secret", secret)
+	}
+	return http.DefaultClient.Do(req)
+}
+
+// --- Tests ---
+
+func TestCheckSecret(t *testing.T) {
+	if !checkSecret("mykey", "mykey") {
+		t.Error("expected match")
+	}
+	if checkSecret("mykey", "wrong") {
+		t.Error("expected no match")
+	}
+	if checkSecret("", "key") {
+		t.Error("expected no match for empty got")
+	}
+}
+
+// --- Push Heartbeat ---
+
+func TestPush_MissingToken(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := http.Get(ts.baseURL + "/api/push")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 400 {
+		t.Errorf("expected 400, got %d", resp.StatusCode)
+	}
+}
+
+func TestPush_InvalidToken(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := http.Get(ts.baseURL + "/api/push?token=bad")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 404 {
+		t.Errorf("expected 404, got %d", resp.StatusCode)
+	}
+}
+
+// --- Health ---
+
+func TestHealth_NoSecret(t *testing.T) {
+	ts := newTestServer(t, "", false)
+	resp, err := http.Get(ts.baseURL + "/api/health")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200 with no cluster key, got %d", resp.StatusCode)
+	}
+}
+
+func TestHealth_ValidSecret(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := authReq("GET", ts.baseURL+"/api/health", "secret", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", resp.StatusCode)
+	}
+}
+
+func TestHealth_WrongSecret(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := authReq("GET", ts.baseURL+"/api/health", "wrong", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 401 {
+		t.Errorf("expected 401, got %d", resp.StatusCode)
+	}
+}
+
+// --- Backup Export ---
+
+func TestExport_Unauthorized_NoKey(t *testing.T) {
+	ts := newTestServer(t, "", false)
+	resp, err := http.Get(ts.baseURL + "/api/backup/export")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 401 {
+		t.Errorf("expected 401 when no cluster key configured, got %d", resp.StatusCode)
+	}
+}
+
+func TestExport_Unauthorized_WrongKey(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := authReq("GET", ts.baseURL+"/api/backup/export", "wrong", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 401 {
+		t.Errorf("expected 401, got %d", resp.StatusCode)
+	}
+}
+
+func TestExport_Success(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	ts.store.sites = []models.Site{{ID: 1, Name: "example", URL: "http://example.com"}}
+
+	resp, err := authReq("GET", ts.baseURL+"/api/backup/export", "secret", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", resp.StatusCode)
+	}
+	var backup models.Backup
+	json.NewDecoder(resp.Body).Decode(&backup)
+	if len(backup.Sites) != 1 {
+		t.Errorf("expected 1 site, got %d", len(backup.Sites))
+	}
+}
+
+// --- Backup Import ---
+
+func TestImport_MethodNotAllowed(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := authReq("GET", ts.baseURL+"/api/backup/import", "secret", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 405 {
+		t.Errorf("expected 405, got %d", resp.StatusCode)
+	}
+}
+
+func TestImport_Unauthorized(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	body, _ := json.Marshal(models.Backup{})
+	resp, err := authReq("POST", ts.baseURL+"/api/backup/import", "wrong", body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 401 {
+		t.Errorf("expected 401, got %d", resp.StatusCode)
+	}
+}
+
+func TestImport_Success(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	backup := models.Backup{
+		Sites: []models.Site{{Name: "imported", URL: "http://example.com"}},
+	}
+	body, _ := json.Marshal(backup)
+	resp, err := authReq("POST", ts.baseURL+"/api/backup/import", "secret", body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", resp.StatusCode)
+	}
+	ts.store.mu.Lock()
+	defer ts.store.mu.Unlock()
+	if ts.store.importedData == nil {
+		t.Error("expected import data to be stored")
+	}
+}
+
+func TestImport_InvalidJSON(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := authReq("POST", ts.baseURL+"/api/backup/import", "secret", []byte("not json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 400 {
+		t.Errorf("expected 400, got %d", resp.StatusCode)
+	}
+}
+
+// --- Probe Registration ---
+
+func TestProbeRegister_Success(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	body, _ := json.Marshal(map[string]string{
+		"id": "node-1", "name": "US East", "region": "us-east",
+	})
+	resp, err := authReq("POST", ts.baseURL+"/api/probe/register", "secret", body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", resp.StatusCode)
+	}
+	ts.store.mu.Lock()
+	defer ts.store.mu.Unlock()
+	if len(ts.store.registeredNodes) != 1 {
+		t.Errorf("expected 1 registered node, got %d", len(ts.store.registeredNodes))
+	}
+	if ts.store.registeredNodes[0].ID != "node-1" {
+		t.Errorf("expected node-1, got %s", ts.store.registeredNodes[0].ID)
+	}
+}
+
+func TestProbeRegister_MissingID(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	body, _ := json.Marshal(map[string]string{"name": "test"})
+	resp, err := authReq("POST", ts.baseURL+"/api/probe/register", "secret", body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 400 {
+		t.Errorf("expected 400, got %d", resp.StatusCode)
+	}
+}
+
+func TestProbeRegister_Unauthorized(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	body, _ := json.Marshal(map[string]string{"id": "node-1"})
+	resp, err := authReq("POST", ts.baseURL+"/api/probe/register", "wrong", body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 401 {
+		t.Errorf("expected 401, got %d", resp.StatusCode)
+	}
+}
+
+// --- Probe Results ---
+
+func TestProbeResults_Success(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	body, _ := json.Marshal(map[string]any{
+		"node_id": "node-1",
+		"results": []map[string]any{
+			{"site_id": 1, "latency_ns": 5000000, "is_up": true},
+		},
+	})
+	resp, err := authReq("POST", ts.baseURL+"/api/probe/results", "secret", body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", resp.StatusCode)
+	}
+}
+
+func TestProbeResults_MissingNodeID(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	body, _ := json.Marshal(map[string]any{
+		"results": []map[string]any{},
+	})
+	resp, err := authReq("POST", ts.baseURL+"/api/probe/results", "secret", body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 400 {
+		t.Errorf("expected 400, got %d", resp.StatusCode)
+	}
+}
+
+// --- Status Page ---
+
+func TestStatusPage_Enabled(t *testing.T) {
+	ts := newTestServer(t, "secret", true)
+	resp, err := http.Get(ts.baseURL + "/status")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", resp.StatusCode)
+	}
+}
+
+func TestStatusJSON_TokensStripped(t *testing.T) {
+	ts := newTestServer(t, "secret", true)
+
+	// Inject a site with a token into engine state
+	ts.engine.UpdateSiteConfig(models.Site{ID: 1, Name: "test", Type: "push", Token: "secret-token", Status: "UP"})
+	// Need to inject directly since UpdateSiteConfig only updates existing
+	func() {
+		ts.engine.RecordHeartbeat("unused") // just to exercise, won't match
+	}()
+
+	resp, err := http.Get(ts.baseURL + "/status/json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", resp.StatusCode)
+	}
+	var state map[string]models.Site
+	json.NewDecoder(resp.Body).Decode(&state)
+	for _, site := range state {
+		if site.Token != "" {
+			t.Error("expected token stripped from status JSON response")
+		}
+	}
+}
+
+func TestStatusJSON_MaintenanceOverride(t *testing.T) {
+	ts := newTestServer(t, "secret", true)
+	ts.store.maintWindows = []models.MaintenanceWindow{
+		{ID: 1, MonitorID: 0, Type: "maintenance", StartTime: time.Now().Add(-1 * time.Hour)},
+	}
+
+	resp, err := http.Get(ts.baseURL + "/status/json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", resp.StatusCode)
+	}
+}
+
+func TestStatusPage_Disabled(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := http.Get(ts.baseURL + "/status")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 404 {
+		t.Errorf("expected 404 when status disabled, got %d", resp.StatusCode)
+	}
+}
+
+// --- Probe Assignments ---
+
+func TestProbeAssignments_Success(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := authReq("GET", ts.baseURL+"/api/probe/assignments", "secret", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("expected 200, got %d", resp.StatusCode)
+	}
+	var result map[string][]models.Site
+	json.NewDecoder(resp.Body).Decode(&result)
+	if _, ok := result["sites"]; !ok {
+		t.Error("expected 'sites' key in response")
+	}
+}
+
+func TestProbeAssignments_Unauthorized(t *testing.T) {
+	ts := newTestServer(t, "secret", false)
+	resp, err := authReq("GET", ts.baseURL+"/api/probe/assignments", "wrong", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 401 {
+		t.Errorf("expected 401, got %d", resp.StatusCode)
+	}
+}

internal/store/postgres.go

@@ -2,6 +2,7 @@ package store
 
 import (
 	"database/sql"
+	"log"
 
 	_ "github.com/lib/pq"
 )
@@ -56,6 +57,21 @@ func (d *PostgresDialect) CreateTablesSQL() []string {
 			message TEXT NOT NULL,
 			created_at TIMESTAMP DEFAULT NOW()
 		)`,
+		`CREATE TABLE IF NOT EXISTS maintenance_windows (
+			id SERIAL PRIMARY KEY,
+			monitor_id INTEGER DEFAULT 0,
+			title TEXT NOT NULL,
+			description TEXT DEFAULT '',
+			type TEXT DEFAULT 'maintenance',
+			start_time TIMESTAMP NOT NULL,
+			end_time TIMESTAMP,
+			created_by TEXT DEFAULT '',
+			created_at TIMESTAMP DEFAULT NOW()
+		)`,
+		`CREATE TABLE IF NOT EXISTS preferences (
+			key TEXT PRIMARY KEY,
+			value TEXT NOT NULL
+		)`,
 	}
 }
 
@@ -84,13 +100,31 @@ func (d *PostgresDialect) UpsertNodeSQL() string {
 func (d *PostgresDialect) ResetSequenceOnEmpty(db *sql.DB, table string) {}
 
 func (d *PostgresDialect) ImportWipe(tx *sql.Tx) {
-	tx.Exec("TRUNCATE TABLE sites RESTART IDENTITY CASCADE")
+	if _, err := tx.Exec("TRUNCATE TABLE sites RESTART IDENTITY CASCADE"); err != nil {
-	tx.Exec("TRUNCATE TABLE alerts RESTART IDENTITY CASCADE")
+		log.Printf("import wipe error: %v", err)
-	tx.Exec("TRUNCATE TABLE users RESTART IDENTITY CASCADE")
+	}
+	if _, err := tx.Exec("TRUNCATE TABLE alerts RESTART IDENTITY CASCADE"); err != nil {
+		log.Printf("import wipe error: %v", err)
+	}
+	if _, err := tx.Exec("TRUNCATE TABLE users RESTART IDENTITY CASCADE"); err != nil {
+		log.Printf("import wipe error: %v", err)
+	}
+	if _, err := tx.Exec("TRUNCATE TABLE maintenance_windows RESTART IDENTITY CASCADE"); err != nil {
+		log.Printf("import wipe error: %v", err)
+	}
 }
 
 func (d *PostgresDialect) ImportResetSequences(tx *sql.Tx) {
-	tx.Exec("SELECT setval('sites_id_seq', (SELECT COALESCE(MAX(id), 1) FROM sites))")
+	if _, err := tx.Exec("SELECT setval('sites_id_seq', (SELECT COALESCE(MAX(id), 1) FROM sites))"); err != nil {
-	tx.Exec("SELECT setval('alerts_id_seq', (SELECT COALESCE(MAX(id), 1) FROM alerts))")
+		log.Printf("sequence reset error: %v", err)
-	tx.Exec("SELECT setval('users_id_seq', (SELECT COALESCE(MAX(id), 1) FROM users))")
+	}
+	if _, err := tx.Exec("SELECT setval('alerts_id_seq', (SELECT COALESCE(MAX(id), 1) FROM alerts))"); err != nil {
+		log.Printf("sequence reset error: %v", err)
+	}
+	if _, err := tx.Exec("SELECT setval('users_id_seq', (SELECT COALESCE(MAX(id), 1) FROM users))"); err != nil {
+		log.Printf("sequence reset error: %v", err)
+	}
+	if _, err := tx.Exec("SELECT setval('maintenance_windows_id_seq', (SELECT COALESCE(MAX(id), 1) FROM maintenance_windows))"); err != nil {
+		log.Printf("sequence reset error: %v", err)
+	}
 }

internal/store/sqlite.go

@@ -2,6 +2,7 @@ package store
 
 import (
 	"database/sql"
+	"log"
 
 	_ "github.com/mattn/go-sqlite3"
 )
@@ -56,6 +57,21 @@ func (d *SQLiteDialect) CreateTablesSQL() []string {
 			message TEXT NOT NULL,
 			created_at DATETIME DEFAULT CURRENT_TIMESTAMP
 		)`,
+		`CREATE TABLE IF NOT EXISTS maintenance_windows (
+			id INTEGER PRIMARY KEY AUTOINCREMENT,
+			monitor_id INTEGER DEFAULT 0,
+			title TEXT NOT NULL,
+			description TEXT DEFAULT '',
+			type TEXT DEFAULT 'maintenance',
+			start_time DATETIME NOT NULL,
+			end_time DATETIME,
+			created_by TEXT DEFAULT '',
+			created_at DATETIME DEFAULT CURRENT_TIMESTAMP
+		)`,
+		`CREATE TABLE IF NOT EXISTS preferences (
+			key TEXT PRIMARY KEY,
+			value TEXT NOT NULL
+		)`,
 	}
 }
 
@@ -83,19 +99,39 @@ func (d *SQLiteDialect) UpsertNodeSQL() string {
 
 func (d *SQLiteDialect) ResetSequenceOnEmpty(db *sql.DB, table string) {
 	var count int
-	db.QueryRow("SELECT COUNT(*) FROM " + table).Scan(&count)
+	_ = db.QueryRow("SELECT COUNT(*) FROM " + table).Scan(&count) //nolint:errcheck
 	if count == 0 {
-		db.Exec("DELETE FROM sqlite_sequence WHERE name=?", table)
+		if _, err := db.Exec("DELETE FROM sqlite_sequence WHERE name=?", table); err != nil {
+			log.Printf("sequence cleanup error: %v", err)
+		}
 	}
 }
 
 func (d *SQLiteDialect) ImportWipe(tx *sql.Tx) {
-	tx.Exec("DELETE FROM sites")
+	if _, err := tx.Exec("DELETE FROM sites"); err != nil {
-	tx.Exec("DELETE FROM sqlite_sequence WHERE name='sites'")
+		log.Printf("import wipe error: %v", err)
-	tx.Exec("DELETE FROM alerts")
+	}
-	tx.Exec("DELETE FROM sqlite_sequence WHERE name='alerts'")
+	if _, err := tx.Exec("DELETE FROM sqlite_sequence WHERE name='sites'"); err != nil {
-	tx.Exec("DELETE FROM users")
+		log.Printf("import wipe error: %v", err)
-	tx.Exec("DELETE FROM sqlite_sequence WHERE name='users'")
+	}
+	if _, err := tx.Exec("DELETE FROM alerts"); err != nil {
+		log.Printf("import wipe error: %v", err)
+	}
+	if _, err := tx.Exec("DELETE FROM sqlite_sequence WHERE name='alerts'"); err != nil {
+		log.Printf("import wipe error: %v", err)
+	}
+	if _, err := tx.Exec("DELETE FROM users"); err != nil {
+		log.Printf("import wipe error: %v", err)
+	}
+	if _, err := tx.Exec("DELETE FROM sqlite_sequence WHERE name='users'"); err != nil {
+		log.Printf("import wipe error: %v", err)
+	}
+	if _, err := tx.Exec("DELETE FROM maintenance_windows"); err != nil {
+		log.Printf("import wipe error: %v", err)
+	}
+	if _, err := tx.Exec("DELETE FROM sqlite_sequence WHERE name='maintenance_windows'"); err != nil {
+		log.Printf("import wipe error: %v", err)
+	}
 }
 
 func (d *SQLiteDialect) ImportResetSequences(tx *sql.Tx) {}

internal/store/sqlstore.go

@@ -7,6 +7,8 @@ import (
 	"encoding/json"
 	"fmt"
 	"go-upkeep/internal/models"
+	"log"
+	"time"
 )
 
 type SQLStore struct {
@@ -28,12 +30,16 @@ func (s *SQLStore) q(query string) string {
 	return rewritePlaceholders(query, s.dollar)
 }
 
-func generateToken() string {
+func generateToken() (string, error) {
 	b := make([]byte, 16)
 	if _, err := rand.Read(b); err != nil {
-		panic("crypto/rand failed: " + err.Error())
+		return "", fmt.Errorf("crypto/rand failed: %w", err)
 	}
-	return hex.EncodeToString(b)
+	return hex.EncodeToString(b), nil
+}
+
+func (s *SQLStore) Close() error {
+	return s.db.Close()
 }
 
 func (s *SQLStore) Init() error {
@@ -43,14 +49,16 @@ func (s *SQLStore) Init() error {
 		}
 	}
 	for _, m := range s.dialect.MigrationsSQL() {
-		s.db.Exec(m)
+		if _, err := s.db.Exec(m); err != nil {
+			log.Printf("migration error: %v", err)
+		}
 	}
 	return nil
 }
 
 func (s *SQLStore) GetSites() ([]models.Site, error) {
 	bf := s.dialect.BoolFalse()
-	query := fmt.Sprintf(
+	query := fmt.Sprintf( //nolint:gosec // bf is a dialect boolean literal, not user input
 		"SELECT id, COALESCE(name, url), url, COALESCE(type, 'http'), COALESCE(token, ''), interval, alert_id, check_ssl, threshold, max_retries, COALESCE(hostname, ''), COALESCE(port, 0), COALESCE(timeout, 0), COALESCE(method, 'GET'), COALESCE(description, ''), COALESCE(parent_id, 0), COALESCE(accepted_codes, '200-299'), COALESCE(dns_resolve_type, ''), COALESCE(dns_server, ''), COALESCE(ignore_tls, %s), COALESCE(paused, %s), COALESCE(regions, '') FROM sites",
 		bf, bf,
 	)
@@ -76,7 +84,11 @@ func (s *SQLStore) GetSites() ([]models.Site, error) {
 func (s *SQLStore) AddSite(site models.Site) error {
 	token := ""
 	if site.Type == "push" {
-		token = generateToken()
+		var err error
+		token, err = generateToken()
+		if err != nil {
+			return fmt.Errorf("generate push token: %w", err)
+		}
 	}
 	_, err := s.db.Exec(s.q("INSERT INTO sites (name, url, type, token, interval, alert_id, check_ssl, threshold, max_retries, hostname, port, timeout, method, description, parent_id, accepted_codes, dns_resolve_type, dns_server, ignore_tls, paused, regions) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"),
 		site.Name, site.URL, site.Type, token, site.Interval, site.AlertID, site.CheckSSL, site.ExpiryThreshold, site.MaxRetries,
@@ -86,9 +98,13 @@ func (s *SQLStore) AddSite(site models.Site) error {
 
 func (s *SQLStore) UpdateSite(site models.Site) error {
 	var existingToken string
-	s.db.QueryRow(s.q("SELECT token FROM sites WHERE id=?"), site.ID).Scan(&existingToken)
+	_ = s.db.QueryRow(s.q("SELECT token FROM sites WHERE id=?"), site.ID).Scan(&existingToken) //nolint:errcheck
 	if site.Type == "push" && existingToken == "" {
-		existingToken = generateToken()
+		var err error
+		existingToken, err = generateToken()
+		if err != nil {
+			return fmt.Errorf("generate push token: %w", err)
+		}
 	}
 	_, err := s.db.Exec(s.q("UPDATE sites SET name=?, url=?, type=?, token=?, interval=?, alert_id=?, check_ssl=?, threshold=?, max_retries=?, hostname=?, port=?, timeout=?, method=?, description=?, parent_id=?, accepted_codes=?, dns_resolve_type=?, dns_server=?, ignore_tls=?, paused=?, regions=? WHERE id=?"),
 		site.Name, site.URL, site.Type, existingToken, site.Interval, site.AlertID, site.CheckSSL, site.ExpiryThreshold, site.MaxRetries,
@@ -112,7 +128,7 @@ func (s *SQLStore) DeleteSite(id int) error {
 
 func (s *SQLStore) GetSiteByName(name string) (models.Site, error) {
 	bf := s.dialect.BoolFalse()
-	query := fmt.Sprintf(
+	query := fmt.Sprintf( //nolint:gosec // bf is a dialect boolean literal, not user input
 		"SELECT id, COALESCE(name, url), url, COALESCE(type, 'http'), COALESCE(token, ''), interval, alert_id, check_ssl, threshold, max_retries, COALESCE(hostname, ''), COALESCE(port, 0), COALESCE(timeout, 0), COALESCE(method, 'GET'), COALESCE(description, ''), COALESCE(parent_id, 0), COALESCE(accepted_codes, '200-299'), COALESCE(dns_resolve_type, ''), COALESCE(dns_server, ''), COALESCE(ignore_tls, %s), COALESCE(paused, %s), COALESCE(regions, '') FROM sites WHERE name = %s",
 		bf, bf, s.q("?"),
 	)
@@ -131,7 +147,9 @@ func (s *SQLStore) GetAlertByName(name string) (models.AlertConfig, error) {
 	if err != nil {
 		return a, err
 	}
-	json.Unmarshal([]byte(settingsJSON), &a.Settings)
+	if err := json.Unmarshal([]byte(settingsJSON), &a.Settings); err != nil {
+		return a, fmt.Errorf("unmarshal alert settings: %w", err)
+	}
 	return a, nil
 }
 
@@ -170,7 +188,9 @@ func (s *SQLStore) GetAllAlerts() ([]models.AlertConfig, error) {
 		if err := rows.Scan(&a.ID, &a.Name, &a.Type, &settingsJSON); err != nil {
 			return alerts, err
 		}
-		json.Unmarshal([]byte(settingsJSON), &a.Settings)
+		if err := json.Unmarshal([]byte(settingsJSON), &a.Settings); err != nil {
+			return alerts, fmt.Errorf("unmarshal alert settings for %q: %w", a.Name, err)
+		}
 		alerts = append(alerts, a)
 	}
 	return alerts, rows.Err()
@@ -183,7 +203,9 @@ func (s *SQLStore) GetAlert(id int) (models.AlertConfig, error) {
 	if err != nil {
 		return a, err
 	}
-	json.Unmarshal([]byte(settingsJSON), &a.Settings)
+	if err := json.Unmarshal([]byte(settingsJSON), &a.Settings); err != nil {
+		return a, fmt.Errorf("unmarshal alert settings: %w", err)
+	}
 	return a, nil
 }
 
@@ -356,6 +378,108 @@ func (s *SQLStore) LoadAllHistory(limit int) (map[int][]models.CheckRecord, erro
 	return result, rows.Err()
 }
 
+func (s *SQLStore) scanMaintenanceWindow(rows *sql.Rows) (models.MaintenanceWindow, error) {
+	var mw models.MaintenanceWindow
+	var endTime sql.NullTime
+	if err := rows.Scan(&mw.ID, &mw.MonitorID, &mw.Title, &mw.Description, &mw.Type, &mw.StartTime, &endTime, &mw.CreatedBy, &mw.CreatedAt); err != nil {
+		return mw, err
+	}
+	if endTime.Valid {
+		mw.EndTime = endTime.Time
+	}
+	return mw, nil
+}
+
+func (s *SQLStore) GetActiveMaintenanceWindows() ([]models.MaintenanceWindow, error) {
+	rows, err := s.db.Query(s.q("SELECT id, monitor_id, title, description, type, start_time, end_time, created_by, created_at FROM maintenance_windows WHERE start_time <= CURRENT_TIMESTAMP AND (end_time IS NULL OR end_time > CURRENT_TIMESTAMP) ORDER BY start_time DESC"))
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var windows []models.MaintenanceWindow
+	for rows.Next() {
+		mw, err := s.scanMaintenanceWindow(rows)
+		if err != nil {
+			return windows, err
+		}
+		windows = append(windows, mw)
+	}
+	return windows, rows.Err()
+}
+
+func (s *SQLStore) GetAllMaintenanceWindows(limit int) ([]models.MaintenanceWindow, error) {
+	rows, err := s.db.Query(s.q("SELECT id, monitor_id, title, description, type, start_time, end_time, created_by, created_at FROM maintenance_windows ORDER BY created_at DESC LIMIT ?"), limit)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var windows []models.MaintenanceWindow
+	for rows.Next() {
+		mw, err := s.scanMaintenanceWindow(rows)
+		if err != nil {
+			return windows, err
+		}
+		windows = append(windows, mw)
+	}
+	return windows, rows.Err()
+}
+
+func (s *SQLStore) AddMaintenanceWindow(mw models.MaintenanceWindow) error {
+	if mw.StartTime.IsZero() {
+		mw.StartTime = time.Now()
+	}
+	_, err := s.db.Exec(s.q("INSERT INTO maintenance_windows (monitor_id, title, description, type, start_time, end_time, created_by) VALUES (?, ?, ?, ?, ?, ?, ?)"),
+		mw.MonitorID, mw.Title, mw.Description, mw.Type, mw.StartTime, sql.NullTime{Time: mw.EndTime, Valid: !mw.EndTime.IsZero()}, mw.CreatedBy)
+	return err
+}
+
+func (s *SQLStore) EndMaintenanceWindow(id int) error {
+	_, err := s.db.Exec(s.q("UPDATE maintenance_windows SET end_time = CURRENT_TIMESTAMP WHERE id = ?"), id)
+	return err
+}
+
+func (s *SQLStore) DeleteMaintenanceWindow(id int) error {
+	_, err := s.db.Exec(s.q("DELETE FROM maintenance_windows WHERE id = ?"), id)
+	if err != nil {
+		return err
+	}
+	s.dialect.ResetSequenceOnEmpty(s.db, "maintenance_windows")
+	return nil
+}
+
+func (s *SQLStore) IsMonitorInMaintenance(monitorID int) (bool, error) {
+	var count int
+	err := s.db.QueryRow(s.q(`SELECT COUNT(*) FROM maintenance_windows
+		WHERE type = 'maintenance'
+		AND start_time <= CURRENT_TIMESTAMP
+		AND (end_time IS NULL OR end_time > CURRENT_TIMESTAMP)
+		AND (monitor_id = 0 OR monitor_id = ?
+			OR monitor_id IN (SELECT parent_id FROM sites WHERE id = ? AND parent_id > 0))`),
+		monitorID, monitorID).Scan(&count)
+	if err != nil {
+		return false, err
+	}
+	return count > 0, nil
+}
+
+func (s *SQLStore) GetPreference(key string) (string, error) {
+	var value string
+	err := s.db.QueryRow(s.q("SELECT value FROM preferences WHERE key = ?"), key).Scan(&value)
+	if err != nil {
+		return "", err
+	}
+	return value, nil
+}
+
+func (s *SQLStore) SetPreference(key, value string) error {
+	if s.dollar {
+		_, err := s.db.Exec(s.q("INSERT INTO preferences (key, value) VALUES (?, ?) ON CONFLICT (key) DO UPDATE SET value = ?"), key, value, value)
+		return err
+	}
+	_, err := s.db.Exec("INSERT OR REPLACE INTO preferences (key, value) VALUES (?, ?)", key, value)
+	return err
+}
+
 func (s *SQLStore) ExportData() (models.Backup, error) {
 	sites, err := s.GetSites()
 	if err != nil {
@@ -369,7 +493,11 @@ func (s *SQLStore) ExportData() (models.Backup, error) {
 	if err != nil {
 		return models.Backup{}, err
 	}
-	return models.Backup{Sites: sites, Alerts: alerts, Users: users}, nil
+	windows, err := s.GetAllMaintenanceWindows(1000)
+	if err != nil {
+		return models.Backup{}, err
+	}
+	return models.Backup{Sites: sites, Alerts: alerts, Users: users, MaintenanceWindows: windows}, nil
 }
 
 func (s *SQLStore) ImportData(data models.Backup) error {
@@ -377,7 +505,7 @@ func (s *SQLStore) ImportData(data models.Backup) error {
 	if err != nil {
 		return err
 	}
-	defer tx.Rollback()
+	defer tx.Rollback() //nolint:errcheck
 
 	s.dialect.ImportWipe(tx)
 
@@ -403,6 +531,13 @@ func (s *SQLStore) ImportData(data models.Backup) error {
 		}
 	}
 
+	for _, mw := range data.MaintenanceWindows {
+		if _, err := tx.Exec(s.q("INSERT INTO maintenance_windows (id, monitor_id, title, description, type, start_time, end_time, created_by) VALUES (?, ?, ?, ?, ?, ?, ?, ?)"),
+			mw.ID, mw.MonitorID, mw.Title, mw.Description, mw.Type, mw.StartTime, sql.NullTime{Time: mw.EndTime, Valid: !mw.EndTime.IsZero()}, mw.CreatedBy); err != nil {
+			return err
+		}
+	}
+
 	s.dialect.ImportResetSequences(tx)
 
 	return tx.Commit()

internal/store/store.go

@@ -49,7 +49,22 @@ type Store interface {
 	SaveLog(message string) error
 	LoadLogs(limit int) ([]string, error)
 
+	// Maintenance Windows
+	GetActiveMaintenanceWindows() ([]models.MaintenanceWindow, error)
+	GetAllMaintenanceWindows(limit int) ([]models.MaintenanceWindow, error)
+	AddMaintenanceWindow(mw models.MaintenanceWindow) error
+	EndMaintenanceWindow(id int) error
+	DeleteMaintenanceWindow(id int) error
+	IsMonitorInMaintenance(monitorID int) (bool, error)
+
+	// Preferences
+	GetPreference(key string) (string, error)
+	SetPreference(key, value string) error
+
 	// Backup & Restore
 	ExportData() (models.Backup, error)
 	ImportData(data models.Backup) error
+
+	// Lifecycle
+	Close() error
 }

internal/tui/tab_maint.go

@@ -0,0 +1,230 @@
+package tui
+
+import (
+	"fmt"
+	"go-upkeep/internal/models"
+	"strconv"
+	"time"
+
+	tea "github.com/charmbracelet/bubbletea"
+	"github.com/charmbracelet/huh"
+	"github.com/charmbracelet/lipgloss"
+)
+
+var maintStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("#bb9af7"))
+
+type maintFormData struct {
+	Title       string
+	Description string
+	Type        string
+	MonitorID   string
+	Duration    string
+	CustomHours string
+}
+
+func fmtMaintStatus(mw models.MaintenanceWindow) string {
+	now := time.Now()
+	if mw.StartTime.After(now) {
+		return warnStyle.Render("SCHEDULED")
+	}
+	if !mw.EndTime.IsZero() && mw.EndTime.Before(now) {
+		return subtleStyle.Render("ENDED")
+	}
+	return specialStyle.Render("ACTIVE")
+}
+
+func fmtMaintType(t string) string {
+	if t == "incident" {
+		return dangerStyle.Render("incident")
+	}
+	return maintStyle.Render("maintenance")
+}
+
+func fmtMaintMonitor(monitorID int, sites []models.Site) string {
+	if monitorID == 0 {
+		return "All"
+	}
+	for _, s := range sites {
+		if s.ID == monitorID {
+			return limitStr(s.Name, 18)
+		}
+	}
+	return fmt.Sprintf("#%d", monitorID)
+}
+
+func fmtMaintTime(t time.Time) string {
+	if t.IsZero() {
+		return subtleStyle.Render("—")
+	}
+	now := time.Now()
+	if t.Year() == now.Year() && t.YearDay() == now.YearDay() {
+		return t.Format("15:04")
+	}
+	return t.Format("15:04 Jan 02")
+}
+
+func (m Model) isMonitorInMaintenance(monitorID int) bool {
+	for _, mw := range m.maintenanceWindows {
+		if mw.Type != "maintenance" {
+			continue
+		}
+		now := time.Now()
+		if mw.StartTime.After(now) {
+			continue
+		}
+		if !mw.EndTime.IsZero() && mw.EndTime.Before(now) {
+			continue
+		}
+		if mw.MonitorID == 0 || mw.MonitorID == monitorID {
+			return true
+		}
+		for _, s := range m.sites {
+			if s.ID == monitorID && s.ParentID > 0 && mw.MonitorID == s.ParentID {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (m Model) viewMaintTab() string {
+	if len(m.maintenanceWindows) == 0 {
+		return "\n  No maintenance windows or incidents. Press [n] to create one."
+	}
+
+	return m.renderTable(
+		[]string{"#", "TITLE", "TYPE", "MONITORS", "STATUS", "STARTED", "ENDS"},
+		len(m.maintenanceWindows),
+		func(start, end int) [][]string {
+			var rows [][]string
+			allSites := m.engine.GetAllSites()
+			for i := start; i < end; i++ {
+				mw := m.maintenanceWindows[i]
+				rows = append(rows, []string{
+					strconv.Itoa(i + 1),
+					m.zones.Mark(fmt.Sprintf("maint-%d", i), limitStr(mw.Title, 24)),
+					fmtMaintType(mw.Type),
+					fmtMaintMonitor(mw.MonitorID, allSites),
+					fmtMaintStatus(mw),
+					fmtMaintTime(mw.StartTime),
+					fmtMaintTime(mw.EndTime),
+				})
+			}
+			return rows
+		},
+		[]int{6, 0, 14, 20, 12, 16, 16},
+		nil,
+	)
+}
+
+func (m *Model) initMaintHuhForm() tea.Cmd {
+	m.maintFormData = &maintFormData{
+		Type:        "maintenance",
+		MonitorID:   "0",
+		Duration:    "1h",
+		CustomHours: "12",
+	}
+
+	monitorOpts := []huh.Option[string]{huh.NewOption("All Monitors", "0")}
+	allSites := m.engine.GetAllSites()
+	for _, s := range allSites {
+		label := s.Name
+		if s.Type == "group" {
+			label = s.Name + " (group)"
+		}
+		monitorOpts = append(monitorOpts, huh.NewOption(label, strconv.Itoa(s.ID)))
+	}
+
+	m.huhForm = huh.NewForm(
+		huh.NewGroup(
+			huh.NewInput().Title("Title").
+				Placeholder("DB Migration").
+				Value(&m.maintFormData.Title).
+				Validate(func(s string) error {
+					if s == "" {
+						return fmt.Errorf("title is required")
+					}
+					return nil
+				}),
+			huh.NewSelect[string]().Title("Type").
+				Options(
+					huh.NewOption("Maintenance (suppress alerts)", "maintenance"),
+					huh.NewOption("Incident (informational)", "incident"),
+				).Value(&m.maintFormData.Type),
+			huh.NewSelect[string]().Title("Affected Monitors").
+				Options(monitorOpts...).
+				Value(&m.maintFormData.MonitorID),
+			huh.NewInput().Title("Description").
+				Placeholder("Optional notes").
+				Value(&m.maintFormData.Description),
+		).Title("Maintenance Window"),
+		huh.NewGroup(
+			huh.NewSelect[string]().Title("Duration").
+				Options(
+					huh.NewOption("1 hour", "1h"),
+					huh.NewOption("2 hours", "2h"),
+					huh.NewOption("4 hours", "4h"),
+					huh.NewOption("8 hours", "8h"),
+					huh.NewOption("Indefinite (end manually)", "indefinite"),
+					huh.NewOption("Custom", "custom"),
+				).Value(&m.maintFormData.Duration),
+			huh.NewInput().Title("Custom Duration (hours)").
+				Placeholder("12").
+				Value(&m.maintFormData.CustomHours).
+				Validate(func(s string) error {
+					if m.maintFormData.Duration != "custom" {
+						return nil
+					}
+					v, err := strconv.Atoi(s)
+					if err != nil {
+						return fmt.Errorf("must be a number")
+					}
+					if v < 1 {
+						return fmt.Errorf("must be at least 1 hour")
+					}
+					return nil
+				}),
+		).Title("Duration").WithHideFunc(func() bool {
+			return m.maintFormData.Type == "incident"
+		}),
+	).WithTheme(huh.ThemeDracula())
+
+	return m.huhForm.Init()
+}
+
+func (m *Model) submitMaintForm() {
+	d := m.maintFormData
+	monitorID, _ := strconv.Atoi(d.MonitorID)
+
+	mw := models.MaintenanceWindow{
+		MonitorID:   monitorID,
+		Title:       d.Title,
+		Description: d.Description,
+		Type:        d.Type,
+		StartTime:   time.Now(),
+	}
+
+	if d.Type == "maintenance" {
+		switch d.Duration {
+		case "1h":
+			mw.EndTime = mw.StartTime.Add(1 * time.Hour)
+		case "2h":
+			mw.EndTime = mw.StartTime.Add(2 * time.Hour)
+		case "4h":
+			mw.EndTime = mw.StartTime.Add(4 * time.Hour)
+		case "8h":
+			mw.EndTime = mw.StartTime.Add(8 * time.Hour)
+		case "custom":
+			hours, _ := strconv.Atoi(d.CustomHours)
+			if hours < 1 {
+				hours = 1
+			}
+			mw.EndTime = mw.StartTime.Add(time.Duration(hours) * time.Hour)
+		}
+	}
+
+	if err := m.store.AddMaintenanceWindow(mw); err != nil {
+		m.engine.AddLog("Add maintenance window failed: " + err.Error())
+	}
+	m.state = stateDashboard
+}

internal/tui/tab_nodes.go

@@ -2,8 +2,6 @@ package tui
 
 import (
 	"fmt"
-	"go-upkeep/internal/models"
-	"strings"
 	"time"
 )
 
@@ -71,26 +69,3 @@ func fmtNodeLastSeen(t time.Time) string {
 	}
 	return fmt.Sprintf("%dh ago", int(ago.Hours()))
 }
-
-func fmtProbeRegions(site models.Site, probeResults map[string]probeStatus) string {
-	if len(probeResults) == 0 {
-		return subtleStyle.Render("—")
-	}
-	var parts []string
-	for region, status := range probeResults {
-		short := region
-		if len(short) > 6 {
-			short = short[:6]
-		}
-		if status.isUp {
-			parts = append(parts, specialStyle.Render(short+":UP"))
-		} else {
-			parts = append(parts, dangerStyle.Render(short+":DN"))
-		}
-	}
-	return strings.Join(parts, " ")
-}
-
-type probeStatus struct {
-	isUp bool
-}

internal/tui/tab_sites.go

@@ -29,9 +29,9 @@ func typeIcon(siteType string, collapsed bool) string {
 		return "◆"
 	case "group":
 		if collapsed {
-			return ""
+			return "▶"
 		}
-		return ""
+		return "▼"
 	default:
 		return "·"
 	}
@@ -132,6 +132,93 @@ func heartbeatSparkline(statuses []bool, width int) string {
 	return sb.String()
 }
 
+func (m Model) groupSparkline(groupID int, width int) string {
+	allSites := m.engine.GetAllSites()
+	var childStatuses [][]bool
+	for _, s := range allSites {
+		if s.ParentID == groupID && !s.Paused && !m.isMonitorInMaintenance(s.ID) {
+			hist, _ := m.engine.GetHistory(s.ID)
+			if len(hist.Statuses) > 0 {
+				childStatuses = append(childStatuses, hist.Statuses)
+			}
+		}
+	}
+
+	if len(childStatuses) == 0 {
+		return subtleStyle.Render(strings.Repeat("·", width))
+	}
+
+	maxLen := 0
+	for _, s := range childStatuses {
+		if len(s) > maxLen {
+			maxLen = len(s)
+		}
+	}
+	if maxLen > width {
+		maxLen = width
+	}
+
+	aggregated := make([]bool, maxLen)
+	for i := 0; i < maxLen; i++ {
+		allUp := true
+		for _, statuses := range childStatuses {
+			idx := len(statuses) - maxLen + i
+			if idx >= 0 && !statuses[idx] {
+				allUp = false
+				break
+			}
+		}
+		aggregated[i] = allUp
+	}
+
+	var sb strings.Builder
+	if remaining := width - len(aggregated); remaining > 0 {
+		sb.WriteString(subtleStyle.Render(strings.Repeat("·", remaining)))
+	}
+	for _, up := range aggregated {
+		if up {
+			sb.WriteString(specialStyle.Render("●"))
+		} else {
+			sb.WriteString(dangerStyle.Render("●"))
+		}
+	}
+	return sb.String()
+}
+
+func (m Model) groupUptime(groupID int) string {
+	allSites := m.engine.GetAllSites()
+	var allStatuses [][]bool
+	for _, s := range allSites {
+		if s.ParentID == groupID && !s.Paused && !m.isMonitorInMaintenance(s.ID) {
+			hist, _ := m.engine.GetHistory(s.ID)
+			if len(hist.Statuses) > 0 {
+				allStatuses = append(allStatuses, hist.Statuses)
+			}
+		}
+	}
+	if len(allStatuses) == 0 {
+		return subtleStyle.Render("—")
+	}
+	total, up := 0, 0
+	for _, statuses := range allStatuses {
+		for _, s := range statuses {
+			total++
+			if s {
+				up++
+			}
+		}
+	}
+	return fmtUptime(func() []bool {
+		out := make([]bool, total)
+		idx := 0
+		for _, statuses := range allStatuses {
+			copy(out[idx:], statuses)
+			idx += len(statuses)
+		}
+		return out
+	}())
+}
+
 func fmtLatency(d time.Duration) string {
 	ms := d.Milliseconds()
 	if ms == 0 {
@@ -207,14 +294,17 @@ func fmtRetries(site models.Site) string {
 	return s
 }
 
-func fmtStatus(status string, paused bool) string {
+func fmtStatus(status string, paused bool, inMaint bool) string {
 	if paused {
 		return warnStyle.Render("PAUSED")
 	}
-	switch {
+	if inMaint {
-	case status == "DOWN" || status == "SSL EXP":
+		return maintStyle.Render("MAINT")
+	}
+	switch status {
+	case "DOWN", "SSL EXP":
 		return dangerStyle.Render(status)
-	case status == "PENDING":
+	case "PENDING":
 		return subtleStyle.Render(status)
 	default:
 		return specialStyle.Render(status)
@@ -224,7 +314,7 @@ func fmtStatus(status string, paused bool) string {
 func (m Model) dynamicWidths() (nameW, sparkW int) {
 	fixed := 6 + 10 + 10 + 8 + 8 + 7 + 9 // #, TYPE, STATUS, LATENCY, UPTIME, SSL, RETRY
 	overhead := 30                       // cell padding + borders
-	avail := m.termWidth - 6 - fixed - overhead
+	avail := m.termWidth - chromePadH - 2 - fixed - overhead
 	if avail < 30 {
 		avail = 30
 	}
@@ -280,10 +370,10 @@ func (m Model) viewSitesTab() string {
 						strconv.Itoa(i + 1),
 						m.zones.Mark(fmt.Sprintf("site-%d", i), icon+" "+limitStr(site.Name, nameW-2)),
 						"group",
-						fmtStatus(site.Status, site.Paused),
+						fmtStatus(site.Status, site.Paused, m.isMonitorInMaintenance(site.ID)),
 						subtleStyle.Render("—"),
-						subtleStyle.Render("—"),
+						m.groupUptime(site.ID),
-						subtleStyle.Render(strings.Repeat("·", sparkWidth)),
+						m.groupSparkline(site.ID, sparkWidth),
 						subtleStyle.Render("-"),
 						subtleStyle.Render("—"),
 					})
@@ -313,7 +403,7 @@ func (m Model) viewSitesTab() string {
 					strconv.Itoa(i + 1),
 					m.zones.Mark(fmt.Sprintf("site-%d", i), name),
 					typeIcon(site.Type, false) + " " + site.Type,
-					fmtStatus(site.Status, site.Paused),
+					fmtStatus(site.Status, site.Paused, m.isMonitorInMaintenance(site.ID)),
 					fmtLatency(site.Latency),
 					fmtUptime(hist.Statuses),
 					spark,
@@ -616,14 +706,33 @@ func (m Model) viewDetailPanel() string {
 
 	var b strings.Builder
 
-	title := titleStyle.Render(fmt.Sprintf("  %s", site.Name))
+	var breadcrumb string
-	b.WriteString(title + "\n\n")
+	if site.ParentID > 0 {
+		for _, s := range m.sites {
+			if s.ID == site.ParentID {
+				breadcrumb = subtleStyle.Render("  Sites > "+s.Name+" > ") + titleStyle.Render(site.Name)
+				break
+			}
+		}
+	}
+	if breadcrumb == "" {
+		breadcrumb = subtleStyle.Render("  Sites > ") + titleStyle.Render(site.Name)
+	}
+	b.WriteString(breadcrumb + "\n\n")
 
 	row := func(label, value string) {
-		b.WriteString(fmt.Sprintf("  %-16s %s\n", subtleStyle.Render(label), value))
+		fmt.Fprintf(&b, "  %-16s %s\n", subtleStyle.Render(label), value)
 	}
 
-	row("Status", fmtStatus(site.Status, site.Paused))
+	row("Status", fmtStatus(site.Status, site.Paused, m.isMonitorInMaintenance(site.ID)))
+	if m.isMonitorInMaintenance(site.ID) {
+		for _, mw := range m.maintenanceWindows {
+			if mw.Type == "maintenance" && (mw.MonitorID == 0 || mw.MonitorID == site.ID || mw.MonitorID == site.ParentID) {
+				row("Maintenance", maintStyle.Render(mw.Title))
+				break
+			}
+		}
+	}
 	row("Type", site.Type)
 	if site.URL != "" {
 		row("URL", site.URL)
@@ -671,7 +780,7 @@ func (m Model) viewDetailPanel() string {
 			}
 			latency := time.Duration(result.LatencyNs).Milliseconds()
 			ago := time.Since(result.CheckedAt).Truncate(time.Second)
-			b.WriteString(fmt.Sprintf("  %-14s %s  %dms  %s ago\n", nodeID, status, latency, ago))
+			fmt.Fprintf(&b, "  %-14s %s  %dms  %s ago\n", nodeID, status, latency, ago)
 		}
 	}
 
@@ -679,8 +788,37 @@ func (m Model) viewDetailPanel() string {
 	const sparkWidth = 40
 	if site.Type == "push" {
 		b.WriteString("  " + heartbeatSparkline(hist.Statuses, sparkWidth))
+		if len(hist.Statuses) > 0 {
+			up := 0
+			for _, s := range hist.Statuses {
+				if s {
+					up++
+				}
+			}
+			fmt.Fprintf(&b, "\n  %s %d/%d checks up",
+				subtleStyle.Render("Heartbeats"),
+				up, len(hist.Statuses))
+		}
 	} else {
 		b.WriteString("  " + latencySparkline(hist.Latencies, sparkWidth))
+		if len(hist.Latencies) > 0 {
+			minL, maxL := hist.Latencies[0], hist.Latencies[0]
+			var total time.Duration
+			for _, l := range hist.Latencies {
+				total += l
+				if l < minL {
+					minL = l
+				}
+				if l > maxL {
+					maxL = l
+				}
+			}
+			avg := total / time.Duration(len(hist.Latencies))
+			fmt.Fprintf(&b, "\n  %s %dms  %s %dms  %s %dms",
+				subtleStyle.Render("Min"), minL.Milliseconds(),
+				subtleStyle.Render("Avg"), avg.Milliseconds(),
+				subtleStyle.Render("Max"), maxL.Milliseconds())
+		}
 	}
 
 	b.WriteString("\n\n")

internal/tui/table_helpers.go

@@ -21,6 +21,10 @@ var (
 
 	tableBorderStyle = lipgloss.NewStyle().
 				Foreground(lipgloss.Color("#444"))
+
+	tableZebraStyle = lipgloss.NewStyle().
+			Padding(0, 1).
+			Background(lipgloss.Color("#1a1a2e"))
 )
 
 type StyleOverride func(row, col int) *lipgloss.Style
@@ -38,7 +42,7 @@ func (m Model) renderTable(headers []string, items int, buildRows func(start, en
 	selectedVisual := m.cursor - m.tableOffset
 	rows := buildRows(m.tableOffset, end)
 
-	tableWidth := m.termWidth - 6
+	tableWidth := m.termWidth - chromePadH - 2
 	if tableWidth < 40 {
 		tableWidth = 40
 	}
@@ -53,16 +57,24 @@ func (m Model) renderTable(headers []string, items int, buildRows func(start, en
 			if row == table.HeaderRow {
 				return tableHeaderStyle
 			}
+			isSelected := row == selectedVisual
 			if styleOverride != nil {
 				if s := styleOverride(row, col); s != nil {
-					if col < len(colWidths) && colWidths[col] > 0 {
+					style := *s
-						return s.Width(colWidths[col])
+					if isSelected {
+						style = tableSelectedStyle.Foreground(s.GetForeground())
 					}
-					return *s
+					if col < len(colWidths) && colWidths[col] > 0 {
+						style = style.Width(colWidths[col])
+					}
+					return style
 				}
 			}
 			base := tableCellStyle
-			if row == selectedVisual {
+			if row%2 == 1 {
+				base = tableZebraStyle
+			}
+			if isSelected {
 				base = tableSelectedStyle
 			}
 			if col < len(colWidths) && colWidths[col] > 0 {

internal/tui/tui.go

@@ -1,6 +1,7 @@
 package tui
 
 import (
+	"encoding/json"
 	"fmt"
 	"go-upkeep/internal/models"
 	"go-upkeep/internal/monitor"
@@ -31,6 +32,16 @@ var (
 
 var pulseFrames = []string{"⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"}
 
+const (
+	chromePadV   = 2 // outer Padding(1,2): 1 top + 1 bottom
+	chromePadH   = 4 // outer Padding(1,2): 2 left + 2 right
+	chromeHeader = 1 // tab bar line
+	chromeGaps   = 2 // "\n" separators: before content + before footer
+	chromeFooter = 2 // footer: "\n" prefix + text line
+	chromeTable  = 3 // renderTable "\n" prefix + top border + header + bottom border (lipgloss collapses two into three rendered lines)
+	chromeBase   = chromePadV + chromeHeader + chromeGaps + chromeFooter + chromeTable
+)
+
 type sessionState int
 
 const (
@@ -42,6 +53,7 @@ const (
 	stateFormAlert
 	stateFormUser
 	stateConfirmDelete
+	stateFormMaint
 )
 
 type Model struct {
@@ -59,6 +71,7 @@ type Model struct {
 	siteFormData  *siteFormData
 	alertFormData *alertFormData
 	userFormData  *userFormData
+	maintFormData *maintFormData
 
 	logViewport viewport.Model
 	isAdmin     bool
@@ -78,10 +91,11 @@ type Model struct {
 	pulseVel    float64
 	tickCount   int
 
-	sites  []models.Site
+	sites              []models.Site
-	alerts []models.AlertConfig
+	alerts             []models.AlertConfig
-	users  []models.User
+	users              []models.User
-	nodes  []models.ProbeNode
+	nodes              []models.ProbeNode
+	maintenanceWindows []models.MaintenanceWindow
 
 	filterMode bool
 	filterText string
@@ -92,6 +106,7 @@ func InitialModel(isAdmin bool, s store.Store, eng *monitor.Engine) Model {
 	vpLogs.SetContent("Waiting for logs...")
 	z := zone.New()
 	spring := harmonica.NewSpring(harmonica.FPS(10), 6.0, 0.4)
+	collapsed := loadCollapsed(s)
 	return Model{
 		state:        stateDashboard,
 		logViewport:  vpLogs,
@@ -101,10 +116,37 @@ func InitialModel(isAdmin bool, s store.Store, eng *monitor.Engine) Model {
 		engine:       eng,
 		zones:        z,
 		pulseSpring:  spring,
-		collapsed:    make(map[int]bool),
+		collapsed:    collapsed,
 	}
 }
 
+func loadCollapsed(s store.Store) map[int]bool {
+	m := make(map[int]bool)
+	raw, err := s.GetPreference("collapsed_groups")
+	if err != nil || raw == "" {
+		return m
+	}
+	var ids []int
+	if err := json.Unmarshal([]byte(raw), &ids); err != nil {
+		return m
+	}
+	for _, id := range ids {
+		m[id] = true
+	}
+	return m
+}
+
+func saveCollapsed(s store.Store, collapsed map[int]bool) {
+	var ids []int
+	for id, v := range collapsed {
+		if v {
+			ids = append(ids, id)
+		}
+	}
+	data, _ := json.Marshal(ids)
+	_ = s.SetPreference("collapsed_groups", string(data))
+}
+
 func (m Model) Init() tea.Cmd {
 	return tea.Batch(tea.ClearScreen, tea.Tick(time.Second, func(t time.Time) tea.Msg { return t }))
 }
@@ -128,7 +170,12 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 						m.engine.AddLog("Delete alert failed: " + err.Error())
 					}
 					m.adjustCursor(len(m.alerts) - 1)
-				case 3:
+				case 4:
+					if err := m.store.DeleteMaintenanceWindow(m.deleteID); err != nil {
+						m.engine.AddLog("Delete maintenance window failed: " + err.Error())
+					}
+					m.adjustCursor(len(m.maintenanceWindows) - 1)
+				case 5:
 					if err := m.store.DeleteUser(m.deleteID); err != nil {
 						m.engine.AddLog("Delete user failed: " + err.Error())
 					}
@@ -136,12 +183,12 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				}
 				m.refreshData()
 				m.state = stateDashboard
-				if m.deleteTab == 4 {
+				if m.deleteTab == 5 {
 					m.state = stateUsers
 				}
 			case "n", "N", "esc":
 				m.state = stateDashboard
-				if m.deleteTab == 4 {
+				if m.deleteTab == 5 {
 					m.state = stateUsers
 				}
 			case "ctrl+c":
@@ -152,7 +199,11 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	}
 
 	// Form state: forward ALL messages to huh (keys, timers, resize, etc.)
-	if m.state == stateFormSite || m.state == stateFormAlert || m.state == stateFormUser {
+	if m.state == stateFormSite || m.state == stateFormAlert || m.state == stateFormUser || m.state == stateFormMaint {
+		if wsm, ok := msg.(tea.WindowSizeMsg); ok {
+			m.termWidth = wsm.Width
+			m.termHeight = wsm.Height
+		}
 		if keyMsg, ok := msg.(tea.KeyMsg); ok {
 			if keyMsg.String() == "ctrl+c" {
 				return m, tea.Quit
@@ -160,7 +211,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			if keyMsg.String() == "esc" {
 				m.huhForm = nil
 				m.state = stateDashboard
-				if m.currentTab == 4 {
+				if m.currentTab == 5 {
 					m.state = stateUsers
 				}
 				return m, nil
@@ -186,12 +237,16 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	case tea.WindowSizeMsg:
 		m.termWidth = msg.Width
 		m.termHeight = msg.Height
-		m.maxTableRows = msg.Height - 12
+		chrome := chromeBase
+		if m.filterMode || m.filterText != "" {
+			chrome++
+		}
+		m.maxTableRows = msg.Height - chrome
 		if m.maxTableRows < 1 {
 			m.maxTableRows = 1
 		}
-		m.logViewport.Width = msg.Width
+		m.logViewport.Width = msg.Width - chromePadH
-		m.logViewport.Height = msg.Height - 6
+		m.logViewport.Height = msg.Height - (chromePadV + chromeHeader + chromeGaps + chromeFooter)
 		return m, tea.ClearScreen
 
 	case time.Time:
@@ -209,18 +264,21 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			if msg.Button == tea.MouseButtonWheelUp || msg.Button == tea.MouseButtonWheelDown {
 				if m.state == stateLogs {
 					if msg.Button == tea.MouseButtonWheelUp {
-						m.logViewport.LineUp(3)
+						m.logViewport.ScrollUp(3)
 					} else {
-						m.logViewport.LineDown(3)
+						m.logViewport.ScrollDown(3)
 					}
 					return m, nil
 				}
 				listLen := len(m.sites)
-				if m.currentTab == 1 {
+				switch m.currentTab {
+				case 1:
 					listLen = len(m.alerts)
-				} else if m.currentTab == 3 {
+				case 3:
 					listLen = len(m.nodes)
-				} else if m.currentTab == 4 {
+				case 4:
+					listLen = len(m.maintenanceWindows)
+				case 5:
 					listLen = len(m.users)
 				}
 				if msg.Button == tea.MouseButtonWheelUp {
@@ -307,7 +365,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				}
 			case "up", "k":
 				if m.state == stateLogs {
-					m.logViewport.LineUp(1)
+					m.logViewport.ScrollUp(1)
 				} else if m.cursor > 0 {
 					m.cursor--
 					if m.cursor < m.tableOffset {
@@ -316,7 +374,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				}
 			case "down", "j":
 				if m.state == stateLogs {
-					m.logViewport.LineDown(1)
+					m.logViewport.ScrollDown(1)
 				} else {
 					max := len(m.sites) - 1
 					if m.currentTab == 1 {
@@ -326,6 +384,9 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 						max = len(m.nodes) - 1
 					}
 					if m.currentTab == 4 {
+						max = len(m.maintenanceWindows) - 1
+					}
+					if m.currentTab == 5 {
 						max = len(m.users) - 1
 					}
 					if m.cursor < max {
@@ -344,7 +405,10 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				} else if m.currentTab == 1 {
 					m.state = stateFormAlert
 					return m, m.initAlertHuhForm()
-				} else if m.currentTab == 4 && m.isAdmin {
+				} else if m.currentTab == 4 {
+					m.state = stateFormMaint
+					return m, m.initMaintHuhForm()
+				} else if m.currentTab == 5 && m.isAdmin {
 					m.state = stateFormUser
 					return m, m.initUserHuhForm()
 				}
@@ -358,7 +422,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 					m.editID = m.alerts[m.cursor].ID
 					m.state = stateFormAlert
 					return m, m.initAlertHuhForm()
-				} else if m.currentTab == 4 && m.isAdmin && len(m.users) > 0 {
+				} else if m.currentTab == 5 && m.isAdmin && len(m.users) > 0 {
 					m.editID = m.users[m.cursor].ID
 					m.state = stateFormUser
 					return m, m.initUserHuhForm()
@@ -367,6 +431,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				if m.currentTab == 0 && len(m.sites) > 0 && m.sites[m.cursor].Type == "group" {
 					gid := m.sites[m.cursor].ID
 					m.collapsed[gid] = !m.collapsed[gid]
+					saveCollapsed(m.store, m.collapsed)
 					m.refreshData()
 				}
 			case "p":
@@ -381,6 +446,18 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				if m.currentTab == 0 && len(m.sites) > 0 {
 					m.state = stateDetail
 				}
+			case "x":
+				if m.currentTab == 4 && len(m.maintenanceWindows) > 0 {
+					mw := m.maintenanceWindows[m.cursor]
+					now := time.Now()
+					isActive := !mw.StartTime.After(now) && (mw.EndTime.IsZero() || mw.EndTime.After(now))
+					if isActive {
+						if err := m.store.EndMaintenanceWindow(mw.ID); err != nil {
+							m.engine.AddLog("End maintenance failed: " + err.Error())
+						}
+						m.refreshData()
+					}
+				}
 			case "d", "backspace":
 				if m.currentTab == 0 && len(m.sites) > 0 {
 					m.deleteID = m.sites[m.cursor].ID
@@ -392,10 +469,15 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 					m.deleteName = m.alerts[m.cursor].Name
 					m.deleteTab = 1
 					m.state = stateConfirmDelete
-				} else if m.currentTab == 4 && m.isAdmin && len(m.users) > 0 {
+				} else if m.currentTab == 4 && len(m.maintenanceWindows) > 0 {
+					m.deleteID = m.maintenanceWindows[m.cursor].ID
+					m.deleteName = m.maintenanceWindows[m.cursor].Title
+					m.deleteTab = 4
+					m.state = stateConfirmDelete
+				} else if m.currentTab == 5 && m.isAdmin && len(m.users) > 0 {
 					m.deleteID = m.users[m.cursor].ID
 					m.deleteName = m.users[m.cursor].Username
-					m.deleteTab = 4
+					m.deleteTab = 5
 					m.state = stateConfirmDelete
 				}
 			}
@@ -405,9 +487,9 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 }
 
 func (m *Model) handleClick(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
-	tabCount := 4
+	tabCount := 5
 	if m.isAdmin {
-		tabCount = 5
+		tabCount = 6
 	}
 	for i := 0; i < tabCount; i++ {
 		if m.zones.Get(fmt.Sprintf("tab-%d", i)).InBounds(msg) {
@@ -443,6 +525,19 @@ func (m *Model) handleClick(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
 	}
 
 	if m.currentTab == 4 {
+		end := m.tableOffset + m.maxTableRows
+		if end > len(m.maintenanceWindows) {
+			end = len(m.maintenanceWindows)
+		}
+		for i := m.tableOffset; i < end; i++ {
+			if m.zones.Get(fmt.Sprintf("maint-%d", i)).InBounds(msg) {
+				m.cursor = i
+				return m, nil
+			}
+		}
+	}
+
+	if m.currentTab == 5 {
 		end := m.tableOffset + m.maxTableRows
 		if end > len(m.users) {
 			end = len(m.users)
@@ -459,9 +554,9 @@ func (m *Model) handleClick(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
 }
 
 func (m *Model) switchTab(idx int) {
-	maxTabs := 3
+	maxTabs := 4
 	if m.isAdmin {
-		maxTabs = 4
+		maxTabs = 5
 	}
 	if idx > maxTabs {
 		idx = 0
@@ -472,7 +567,7 @@ func (m *Model) switchTab(idx int) {
 	switch idx {
 	case 2:
 		m.state = stateLogs
-	case 4:
+	case 5:
 		m.state = stateUsers
 	default:
 		m.state = stateDashboard
@@ -545,14 +640,20 @@ func (m *Model) refreshData() {
 	if nodes, err := m.store.GetAllNodes(); err == nil {
 		m.nodes = nodes
 	}
+	if windows, err := m.store.GetAllMaintenanceWindows(100); err == nil {
+		m.maintenanceWindows = windows
+	}
 	m.logViewport.SetContent(strings.Join(m.engine.GetLogs(), "\n"))
 
 	listLen := len(m.sites)
-	if m.currentTab == 1 {
+	switch m.currentTab {
+	case 1:
 		listLen = len(m.alerts)
-	} else if m.currentTab == 3 {
+	case 3:
 		listLen = len(m.nodes)
-	} else if m.currentTab == 4 {
+	case 4:
+		listLen = len(m.maintenanceWindows)
+	case 5:
 		listLen = len(m.users)
 	}
 	if listLen > 0 && m.cursor >= listLen {
@@ -577,6 +678,10 @@ func (m *Model) submitForm() {
 		if m.userFormData != nil {
 			m.submitUserForm()
 		}
+	case stateFormMaint:
+		if m.maintFormData != nil {
+			m.submitMaintForm()
+		}
 	}
 }
 
@@ -588,7 +693,7 @@ func (m Model) pulseIndicator() string {
 	}
 	hasDown := false
 	for _, s := range m.sites {
-		if !s.Paused && (s.Status == "DOWN" || s.Status == "SSL EXP") {
+		if !s.Paused && !m.isMonitorInMaintenance(s.ID) && (s.Status == "DOWN" || s.Status == "SSL EXP") {
 			hasDown = true
 			break
 		}
@@ -606,9 +711,12 @@ func (m Model) View() string {
 	switch m.state {
 	case stateConfirmDelete:
 		kind := "monitor"
-		if m.deleteTab == 1 {
+		switch m.deleteTab {
+		case 1:
 			kind = "alert"
-		} else if m.deleteTab == 4 {
+		case 4:
+			kind = "maintenance window"
+		case 5:
 			kind = "user"
 		}
 		msg := dangerStyle.Render(fmt.Sprintf("Delete %s \"%s\"?", kind, m.deleteName))
@@ -619,7 +727,7 @@ func (m Model) View() string {
 			Padding(1, 3).
 			Render(msg + "\n\n" + hint)
 		return lipgloss.NewStyle().Padding(2, 4).Render(box)
-	case stateFormSite, stateFormAlert, stateFormUser:
+	case stateFormSite, stateFormAlert, stateFormUser, stateFormMaint:
 		if m.huhForm != nil {
 			title := ""
 			switch m.state {
@@ -638,7 +746,14 @@ func (m Model) View() string {
 				if m.editID > 0 {
 					title = fmt.Sprintf("Edit User #%d", m.editID)
 				}
+			case stateFormMaint:
+				title = "New Maintenance Window"
 			}
+			formHeight := m.termHeight - 7
+			if formHeight < 5 {
+				formHeight = 5
+			}
+			m.huhForm.WithHeight(formHeight)
 			header := titleStyle.Render(title)
 			footer := subtleStyle.Render("\n[Esc] Cancel")
 			return lipgloss.NewStyle().Padding(1, 2).Render(header + "\n\n" + m.huhForm.View() + "\n" + footer)
@@ -652,9 +767,15 @@ func (m Model) View() string {
 }
 
 func (m Model) viewDashboard() string {
+	allSites := m.engine.GetAllSites()
+	totalMonitors := 0
 	downCount := 0
-	for _, s := range m.sites {
+	for _, s := range allSites {
-		if !s.Paused && (s.Status == "DOWN" || s.Status == "SSL EXP") {
+		if s.Type == "group" {
+			continue
+		}
+		totalMonitors++
+		if !s.Paused && !m.isMonitorInMaintenance(s.ID) && (s.Status == "DOWN" || s.Status == "SSL EXP") {
 			downCount++
 		}
 	}
@@ -668,8 +789,8 @@ func (m Model) viewDashboard() string {
 	var sitesLabel string
 	if downCount > 0 {
 		sitesLabel = fmt.Sprintf("Sites (%d↓)", downCount)
-	} else if len(m.sites) > 0 {
+	} else if totalMonitors > 0 {
-		sitesLabel = fmt.Sprintf("Sites (%d)", len(m.sites))
+		sitesLabel = fmt.Sprintf("Sites (%d)", totalMonitors)
 	} else {
 		sitesLabel = "Sites"
 	}
@@ -682,7 +803,21 @@ func (m Model) viewDashboard() string {
 		nodesLabel = "Nodes"
 	}
 
-	tabs := []string{sitesLabel, "Alerts", "Logs", nodesLabel}
+	activeMaint := 0
+	for _, mw := range m.maintenanceWindows {
+		now := time.Now()
+		if !mw.StartTime.After(now) && (mw.EndTime.IsZero() || mw.EndTime.After(now)) {
+			activeMaint++
+		}
+	}
+	var maintLabel string
+	if activeMaint > 0 {
+		maintLabel = fmt.Sprintf("Maint (%d)", activeMaint)
+	} else {
+		maintLabel = "Maint"
+	}
+
+	tabs := []string{sitesLabel, "Alerts", "Logs", nodesLabel, maintLabel}
 	if m.isAdmin {
 		tabs = append(tabs, "Users")
 	}
@@ -712,17 +847,19 @@ func (m Model) viewDashboard() string {
 	case 3:
 		content = m.viewNodesTab()
 	case 4:
+		content = m.viewMaintTab()
+	case 5:
 		if m.isAdmin {
 			content = m.viewUsersTab()
 		}
 	}
 
-	upCount := len(m.sites) - downCount
+	upCount := totalMonitors - downCount
 	var upStr string
 	if downCount > 0 {
-		upStr = dangerStyle.Render(fmt.Sprintf("%d/%d UP", upCount, len(m.sites)))
+		upStr = dangerStyle.Render(fmt.Sprintf("%d/%d UP", upCount, totalMonitors))
 	} else {
-		upStr = specialStyle.Render(fmt.Sprintf("%d/%d UP", upCount, len(m.sites)))
+		upStr = specialStyle.Render(fmt.Sprintf("%d/%d UP", upCount, totalMonitors))
 	}
 	statusParts := []string{upStr}
 	if len(m.nodes) > 0 {
@@ -746,6 +883,8 @@ func (m Model) viewDashboard() string {
 		case 0:
 			keys = "[/]Filter [n]New [e]Edit [i]Info [d]Del [p]Pause [Tab]Switch [q]Quit"
 		case 4:
+			keys = "[n]New [x]End [d]Del [Tab]Switch [q]Quit"
+		case 5:
 			keys = "[n]Add [d]Revoke [Tab]Switch [q]Quit"
 		default:
 			keys = "[Tab]Switch [q]Quit"