Agent skill

pwa-expert

Progressive Web App development with Service Workers, offline support, and app-like behavior. Use for caching strategies, install prompts, push notifications, background sync. Activate on "PWA", "Service Worker", "offline", "install prompt", "beforeinstallprompt", "manifest.json", "workbox", "cache-first". NOT for native app development (use React Native), general web performance (use performance docs), or server-side rendering.

View SKILL.md on GitHub Repository
Stars 81
Forks 12

Install this agent skill to your Project

npx add-skill https://github.com/curiositech/some_claude_skills/tree/main/.claude/skills/pwa-expert

Metadata

Additional technical details for this skill

tags
pwa service-worker offline caching installable workbox manifest
category
Design & Creative
pairs with 
[
    {
        "skill": "mobile-ux-optimizer",
        "reason": "PWAs target mobile users requiring touch optimization and responsive layout patterns"
    },
    {
        "skill": "caching-strategies",
        "reason": "Service Worker cache strategies (stale-while-revalidate, cache-first) are core PWA patterns"
    },
    {
        "skill": "react-performance-optimizer",
        "reason": "PWA performance budgets require aggressive React optimization for fast initial loads"
    }
]

SKILL.md

Progressive Web App Expert

Build installable, offline-capable web apps with Service Workers, smart caching, and native-like experiences.

When to Use This Skill

  • Making a web app installable on mobile/desktop
  • Implementing offline functionality
  • Setting up Service Worker caching strategies
  • Handling install prompts (beforeinstallprompt)
  • Background sync for offline-first apps
  • Managing PWA update flows
  • Creating web app manifests

When NOT to Use This Skill

  • Native app development → Use React Native, Flutter, or native SDKs
  • General web performance → Use Lighthouse/performance auditing tools
  • Server-side rendering issues → Use Next.js/framework-specific docs
  • Push notifications only → Consider dedicated push notification services
  • Simple static sites → PWA overhead may not be worth it

Core Concepts

What Makes a PWA Installable

  1. HTTPS (or localhost for dev)
  2. Web App Manifest with required fields
  3. Service Worker with fetch handler
  4. Icons (192×192 and 512×512 minimum)

The PWA Stack

┌─────────────────────────────────────────┐
│           Your App (React/Next.js)      │
├─────────────────────────────────────────┤
│         Service Worker (sw.js)          │
│  ┌─────────────┐  ┌─────────────────┐   │
│  │   Cache     │  │  Network Fetch  │   │
│  │   Storage   │  │    Handling     │   │
│  └─────────────┘  └─────────────────┘   │
├─────────────────────────────────────────┤
│          manifest.json                  │
│  (App identity, icons, display mode)    │
└─────────────────────────────────────────┘

Web App Manifest

Complete manifest.json

json
{
  "name": "Junkie Buds 4 Life",
  "short_name": "JB4L",
  "description": "Recovery support app",
  "start_url": "/",
  "scope": "/",
  "display": "standalone",
  "orientation": "portrait-primary",
  "background_color": "#1a1410",
  "theme_color": "#1a1410",
  "icons": [
    {
      "src": "/icons/icon-192.png",
      "sizes": "192x192",
      "type": "image/png",
      "purpose": "any"
    },
    {
      "src": "/icons/icon-512.png",
      "sizes": "512x512",
      "type": "image/png",
      "purpose": "any"
    },
    {
      "src": "/icons/icon-maskable-512.png",
      "sizes": "512x512",
      "type": "image/png",
      "purpose": "maskable"
    }
  ],
  "shortcuts": [
    {
      "name": "Find Meetings",
      "short_name": "Meetings",
      "url": "/meetings?source=shortcut",
      "icons": [{ "src": "/icons/meetings-96.png", "sizes": "96x96" }]
    }
  ]
}

Display Modes

Mode Description
fullscreen No browser UI, full screen
standalone App-like, no URL bar (recommended)
minimal-ui Some browser controls
browser Normal browser tab

Link in HTML

html
<head>
  <link rel="manifest" href="/manifest.json" />
  <meta name="theme-color" content="#1a1410" />
  <meta name="apple-mobile-web-app-capable" content="yes" />
  <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
  <link rel="apple-touch-icon" href="/icons/apple-touch-icon.png" />
</head>

Service Worker Basics

Registration

typescript
// lib/pwa.ts
export async function registerServiceWorker() {
  if ('serviceWorker' in navigator) {
    try {
      const registration = await navigator.serviceWorker.register('/sw.js', {
        scope: '/',
      });
      return registration;
    } catch (error) {
      console.error('SW registration failed:', error);
    }
  }
}

// Call on app mount
useEffect(() => {
  registerServiceWorker();
}, []);

Basic Service Worker Structure

javascript
// public/sw.js
const CACHE_NAME = 'myapp-v1';
const STATIC_ASSETS = ['/', '/offline', '/manifest.json'];

// Install: Cache static assets
self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME).then((cache) => cache.addAll(STATIC_ASSETS))
  );
  self.skipWaiting();
});

// Activate: Clean old caches
self.addEventListener('activate', (event) => {
  event.waitUntil(
    caches.keys().then((keys) =>
      Promise.all(keys.filter((k) => k !== CACHE_NAME).map((k) => caches.delete(k)))
    )
  );
  self.clients.claim();
});

// Fetch: Handle requests (see references for strategies)
self.addEventListener('fetch', (event) => {
  event.respondWith(handleFetch(event.request));
});

See: references/service-worker-patterns.md for caching strategy implementations

Caching Strategies

Strategy Best For Tradeoff
Cache-First Static assets, fonts, images Stale until cache updated
Network-First API data, user content Slower, needs connectivity
Stale-While-Revalidate Balance freshness/speed Background updates
Network-Only Auth, real-time data No offline support
Cache-Only Versioned assets Never updates

See: references/service-worker-patterns.md for full implementations

Install Prompts

Handle the beforeinstallprompt event to show a custom install UI:

typescript
// Basic pattern
const [deferredPrompt, setDeferredPrompt] = useState(null);

useEffect(() => {
  window.addEventListener('beforeinstallprompt', (e) => {
    e.preventDefault();
    setDeferredPrompt(e);
  });
}, []);

const handleInstall = async () => {
  if (deferredPrompt) {
    deferredPrompt.prompt();
    const { outcome } = await deferredPrompt.userChoice;
    // outcome: 'accepted' or 'dismissed'
  }
};

See: references/install-prompt.md for full usePWAInstall hook and component

Offline Experience

Key patterns:

  • Offline page fallback for navigation failures
  • useOnlineStatus hook to detect connectivity
  • Offline banner to inform users

See: references/offline-handling.md for implementations

Background Sync

Queue actions while offline, execute when connectivity returns:

javascript
// In Service Worker
self.addEventListener('sync', (event) => {
  if (event.tag === 'sync-data') {
    event.waitUntil(syncPendingData());
  }
});

// In App - trigger sync
const registration = await navigator.serviceWorker.ready;
await registration.sync.register('sync-data');

See: references/background-sync.md for full IndexedDB integration

Update Flow

Notify users when a new version is available:

typescript
// Basic pattern
registration.addEventListener('updatefound', () => {
  const newWorker = registration.installing;
  newWorker?.addEventListener('statechange', () => {
    if (newWorker.state === 'installed' && navigator.serviceWorker.controller) {
      // New version available - show update prompt
    }
  });
});

See: references/update-flow.md for usePWAUpdate hook and update strategies

Next.js Integration

Options for Next.js PWA:

  1. next-pwa - Works with standard Next.js server
  2. Custom SW - Required for output: 'export' (static sites)
  3. Workbox CLI - Generate SW after build

See: references/nextjs-integration.md for detailed configurations

Quick Reference

Task Solution
Check if installed window.matchMedia('(display-mode: standalone)').matches
Force SW update registration.update()
Clear all caches caches.keys().then(keys => keys.forEach(k => caches.delete(k)))
Check online navigator.onLine
Get SW registration navigator.serviceWorker.ready
Skip waiting self.skipWaiting() in SW
Take control self.clients.claim() in SW

Testing PWA

Chrome DevTools

  1. Application tab → Manifest, Service Workers, Cache Storage
  2. Lighthouse → PWA audit
  3. Network → Offline checkbox to simulate

Debug Checklist

  • Manifest loads (Application → Manifest)
  • SW registered (Application → Service Workers)
  • Cache populated (Application → Cache Storage)
  • Install prompt fires (Console for beforeinstallprompt)
  • Offline page works (Network → Offline)
  • Update flow works (trigger update, verify prompt)

References

Detailed implementations in /references/:

  • service-worker-patterns.md - Caching strategy implementations
  • install-prompt.md - usePWAInstall hook and install component
  • offline-handling.md - Offline page, status hooks, banners
  • background-sync.md - Background sync with IndexedDB
  • update-flow.md - Update detection and user prompts
  • nextjs-integration.md - Next.js PWA configuration options

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