Offline Capability Checker

A Progressive Web App (PWA) is a web application that uses modern browser APIs to deliver a native app-like experience. Offline capability — powered by Service Workers and Cache API — ensures users can access content even without an internet connection. This is crucial for user retention, accessibility in low-connectivity areas, and meeting Google's PWA installability criteria. PWAs with strong offline support see up to 50% higher user engagement.

Our tool performs multiple checks: (1) HTTPS verification — PWA features require a secure context; (2) Web Manifest detection — we scan common manifest paths like /manifest.json and validate required fields (name, icons, start_url, display); (3) Service Worker probing — for same-origin URLs we detect active SW registrations; (4) Offline storage audit — checking Cache API, IndexedDB, and localStorage availability; (5) Icon completeness — verifying that manifest icons cover 192x192 and 512x512 sizes. Cross-origin limitations are clearly noted in results.

Google Chrome requires: (1) The site must be served over HTTPS; (2) A valid Web Manifest with at least name (or short_name), start_url, display (set to standalone, fullscreen, or minimal-ui), and icons including at least 192x192px and 512x512px; (3) An active Service Worker with a fetch handler that provides offline fallback; (4) The SW must be registered from the same origin. Meeting these triggers the browser's install prompt.

Service Workers can intercept and modify network requests, making them a powerful but potentially dangerous API. Browsers require a secure context (HTTPS or localhost) to register Service Workers, ensuring that the SW script hasn't been tampered with in transit. Without HTTPS, the Service Worker API is simply unavailable — this is non-negotiable for any production PWA deployment.

Common caching strategies include: Cache First — serve from cache, fall back to network (best for static assets); Network First — try network, fall back to cache (good for API data); Stale While Revalidate — serve cache instantly while updating in background (ideal for balancing speed and freshness); Cache Only — strictly offline resources. A robust PWA often combines multiple strategies using Workbox or custom SW logic to handle different resource types appropriately.

Open Chrome DevTools → Application tab → Service Workers panel. Here you can see all registered SWs, their status (activated/installing/waiting), scope, and cached resources. Use the Cache Storage section to inspect cached assets. The Manifest panel shows parsed manifest data. For advanced debugging, enable "Update on reload" to force SW updates during development, and use the Network tab to verify which requests are served from cache vs network.

A good score (70-85) means the site has HTTPS, a valid manifest with essential icons, and a registered Service Worker — meeting basic installability. A perfect score (90-100) indicates comprehensive offline strategy: properly scoped SW with fetch handlers, full icon set including maskable icons, optimized caching with versioning, background sync support, push notifications, responsive design, and fast load times. The gap between "good" and "perfect" often lies in fine-tuning cache strategies and completing the icon/meta configuration.

Yes, with some limitations due to browser security policies. We can always verify HTTPS and test URL reachability. For manifest detection, we attempt to fetch common manifest paths — many CDN-hosted sites allow cross-origin manifest access. Service Worker detection is only fully accurate for same-origin URLs; for external sites, we note this limitation. The tool also tests your own browser's PWA support, which helps developers understand the baseline capabilities available to their users.