watchOS Apps Skill

Design before you code — watchOS requires more planning than coding. Keep interactions brief: a few taps, then wrist down.

Architecture

Layer	Technology	Purpose
Main app	SwiftUI + WatchKit	Navigation, direct interaction
Complications	WidgetKit	Watch face data + app launch
Smart Stack	WidgetKit	Swipe-up widget feed
Notifications	UserNotifications	Alerts + actions
Voice	App Intents / SiriKit	Siri + Shortcuts
Health	HealthKit	Sensors, workouts
Background	WKExtensionDelegate	Refresh, network, BLE

1. App Lifecycle

• Independent app: no iOS companion required
• @main + App protocol; WKApplicationDelegateAdaptor for delegate
• Navigation (watchOS 10): NavigationStack, TabView(.verticalPage)
• Background: WKExtensionDelegate.handle(_:) + WKBackgroundTask

2. Complications (WidgetKit)

• Families: .accessoryCircular, .accessoryRectangular, .accessoryInline, .accessoryCorner
• Pattern: TimelineProvider -> TimelineEntry -> SwiftUI View
• Reload: WidgetCenter.shared.reloadTimelines(ofKind:)
• Smart Stack: widgetRelevances(_:) API
• Migration: replace CLKComplicationDataSource with WidgetKit timeline

3. Always On Display

• TimelineView(.periodic(...)) for live updates
• .isLuminanceReduced env value to adapt UI
• Reduce animations/brightness in AOD state

4. Notifications

• Short-look: auto-generated (non-customizable)
• Long-look: WKUserNotificationHostingController; customize sash colors
• Action buttons: UNNotificationCategory + UNNotificationAction
• Interactive: controls in content area without launching app
• Text input suggestions: override suggestionsForResponseToAction(withIdentifier:for:inputLanguage:)
• Foreground actions run where tapped; background actions run on notification's target device

5. Gestures

• Double Tap (Series 9+, Ultra 2): .handGestureShortcut(.primaryAction) — one per scene
• Priority: primary action > scroll view > vertical tabs
• Action Button (Ultra): AppIntent via ActionButtonArticle

6. App Intents & Siri

• AppIntents: preferred for Siri, Shortcuts, Action button, Spotlight
• SiriKit: domain-based interactions only (messaging, media)
• Conform to AppIntent, implement perform(), use @Parameter

7. HealthKit

• Auth: HKHealthStore().requestAuthorization(toShare:read:)
• Workouts: HKWorkoutSession + HKLiveWorkoutBuilder
• Queries: HKSampleQuery, HKStatisticsQuery, HKAnchoredObjectQuery
• Extended Runtime Session needed for sustained workout tracking

8. Background & Runtime

• Background App Refresh: system-scheduled, limited budget
• WKExtendedRuntimeSession: workouts, mindfulness, location tracking
• Background URLSession: survives app close; prefer small payloads
• Complete tasks with setTaskCompletedWithSnapshot(_:)

9. Networking

• Foreground: URLSession.shared or ephemeral
• Background: URLSessionConfiguration.backgroundSessionConfiguration("id") + delegate

10. Auth, Sizes, A11y, Testing

• Auth: Sign in with Apple or PassKit (no password entry)
• Sizes: 40/41/44/45/49mm — use .containerRelativeFrame(), avoid fixed pixels
• Accessibility: accessibilityLabel/hint/value, .accessibilityElement(children:.combine)
• Testing: add watchOS Unit/UI Testing Bundle target, @testable import

watchOS 10 Changes

• Vertical TabView navigation is standard (no NavigationSplitView)
• Smart Stack replaces Dock for widgets
• WidgetKit powers Lock Screen complications AND Smart Stack

Common Patterns

// Double tap
Button("Action") { go() }.handGestureShortcut(.primaryAction)

// WidgetKit complication
struct W: Widget {
    var body: some WidgetConfiguration {
        StaticConfiguration(kind: "id", provider: P()) { e in V(entry: e) }
        .supportedFamilies([.accessoryCircular, .accessoryRectangular])
    }
}

// Extended runtime
let s = WKExtendedRuntimeSession(); s.delegate = self; s.start()

// Background URLSession
let cfg = URLSessionConfiguration.backgroundSessionConfiguration("com.app.bg")
URLSession(configuration: cfg, delegate: self, delegateQueue: nil)
    .downloadTask(with: url).resume()

// Always On
@Environment(\.isLuminanceReduced) var dim

Reference

For full API docs, notification forwarding details, ClockKit migration, HealthKit patterns: read references/watchos-reference.md bundled with this skill.