# Progressive Web App
> Build Progressive Web Apps (PWAs) with offline support, installability, and caching strategies. Trigger whenever the user mentions PWA, service workers, web app manifests, Workbox, 'add to home screen
- Skill: `ranbot-ai/progressive-web-app` (Agent Skill)
- Install (CLI): `npx skillmds add ranbot-ai/progressive-web-app`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ranbot-ai/progressive-web-app/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ranbot-ai (https://skillmd.com/u/ranbot-ai)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/ranbot-ai/progressive-web-app
---
# Progressive Web Apps (PWAs)
## Overview
A Progressive Web App is a web application that uses modern browser capabilities to deliver a fast, reliable, and installable experience — even on unreliable networks. The three required pillars are:
1. **HTTPS** — Required in production for service workers to register (localhost is exempt for development).
2. **Web App Manifest** (`manifest.json`) — Makes the app installable and defines its appearance on device home screens.
3. **Service Worker** (`sw.js`) — A background script that intercepts network requests, manages caches, and enables offline functionality.
## When to Use This Skill
- Use when the user wants their web app to work offline or on unreliable networks.
- Use when building a mobile-first web project where users should be able to install the app to their home screen.
- Use when the user asks about caching strategies, service workers, or improving web app performance and resilience.
- Use when the user mentions Workbox, web app manifests, background sync, or push notifications for the web.
- Use when the user asks "can my website be installed like an app?" or "how do I make my site work offline?" — even if they don't use the word PWA.
## Deliverables Checklist
Every PWA implementation must include these files at minimum:
- [ ] `index.html` — Links manifest, registers service worker
- [ ] `manifest.json` — Full app metadata and icon set
- [ ] `sw.js` — Service worker with install, activate, and fetch handlers
- [ ] `app.js` — Main app logic with SW registration and install prompt handling
- [ ] `offline.html` — Fallback page shown when navigation fails offline (required — missing file will cause install to fail)
---
## Step 1: Web App Manifest (`manifest.json`)
Defines how the app appears when installed. Must be linked from `` via ``.
```json
{
"name": "My Awesome PWA",
"short_name": "MyPWA",
"description": "A fast, offline-capable Progressive Web App.",
"start_url": "/",
"scope": "/",
"display": "standalone",
"orientation": "portrait-primary",
"background_color": "#ffffff",
"theme_color": "#0055ff",
"icons": [
{
"src": "/assets/icons/icon-192x192.png",
"sizes": "192x192",
"type": "image/png",
"purpose": "any maskable"
},
{
"src": "/assets/icons/icon-512x512.png",
"sizes": "512x512",
"type": "image/png",
"purpose": "any maskable"
}
],
"screenshots": [
{
"src": "/assets/screenshots/desktop.png",
"sizes": "1280x720",
"type": "image/png",
"form_factor": "wide"
}
]
}
```
**Key fields:**
- `display`: `standalone` hides browser UI; `minimal-ui` shows minimal controls; `browser` is standard tab.
- `purpose: "maskable"` on icons enables adaptive icons on Android (safe zone matters — keep content in center 80%).
- `screenshots` is optional but required for Chrome's enhanced install dialog on desktop.
---
## Step 2: HTML Shell (`index.html`)
```html
My Awesome PWA
My PWA
Loading...
```
---
## Step 3: Service Worker Registration & Install Prompt (`app.js`)
```javascript
// ─── Service Worker Registration ───────────────────────────────────────────
if ('serviceWorker' in navigator) {
window.addEventListener('load', async () => {
try {
const registration = await navigator.serviceWorker.register('/sw.js');
console.log('[App] SW registered, scope:', registration.scope);
} catch (err) {
console.error('[App] SW registration failed:', err);
}
});
}
// ─── Install Prompt (Add to Home Screen) ───────────────────────────────────
let deferredPrompt;
const installBtn = document.getElementById('install-btn'); // may be null if omitted
// Capture the browser's install prompt — it fires before the browser's own UI
window.addEventListener('beforeinstallprompt', (e) => {
e.preventDefault(); // Stop automatic mini-infobar on mobile
deferredPrompt = e;
if (installBtn) installBtn.hidden = false; // Show your custom install button
});
if (installBt