PWA Readiness Checker

What Makes A Site A PWA

A progressive web app is a website that can be installed like an app: it gets a home screen icon, opens in its own window without the browser bar, and can keep working when the connection drops. Three pieces make that happen. A web app manifest describes the app: its name, icons, colours and how it opens. A service worker is a script that sits between the app and the network and decides what to serve from cache. And the whole thing must run on HTTPS. This checker tests all three, plus the Apple specific tags that still matter on iPhone.

How The Checker Works

1. It fetches the page and looks for <link rel="manifest">.
2. It fetches the manifest, parses it as JSON and checks each member against the Web App Manifest specification and what browsers need to offer installation.
3. It reads the HTML and inline scripts for navigator.serviceWorker.register() and the script path and scope it registers.
4. It fetches that service worker script and reads it for caching patterns: Workbox, precaching, the strategies used (CacheFirst, NetworkFirst, StaleWhileRevalidate), cache names, update behaviour and whether API or JSON responses are cached.
5. It checks for apple-touch-icon and the Apple web app meta tags.

The Readiness Score And Its Rules

Each rule has a fixed weight. A pass earns the full weight, a warning earns half, a fail earns nothing. Weights add up to 100, and a rule that could not be checked is left out.

• Manifest linked and valid JSON: 15. Service worker registered: 15.
• HTTPS: 10. Display mode of standalone, fullscreen or minimal-ui: 10.
• 192 by 192 icon: 8. 512 by 512 icon: 8.
• name or short_name: 5. start_url: 5. Maskable icon: 5.
• Service worker handles fetch: 4.
• theme_color, background_color and id: 3 each.
• scope contains start_url, apple-touch-icon and Apple web app meta: 2 each.

Reading The Service Worker Findings

Caching is where most PWAs go wrong, and it fails quietly. A CacheFirst or StaleWhileRevalidate rule on /api/ or JSON responses means a user can open the app and see yesterday's prices, stock or bookings, with nothing on screen to say so. Static files such as images, fonts and versioned scripts suit cache first. Data suits NetworkFirst with a short timeout, so the cache is only a fallback. The checker also flags a hand written fetch handler that answers every request from cache before the network, which can trap users on an old version.

It notes update behaviour too. Without skipWaiting, a new service worker waits until every tab of the app is closed, which is why some users keep seeing the old version after a deploy.

What To Do Next

• Fix failing manifest rules first. Most take a minute each, and the PWA Manifest Generator can build a complete manifest and icon set.
• Add a maskable icon with the logo inside the central safe zone.
• Set an id now, before people install. Changing it later creates a second app.
• Review every cached route that returns data.
• Confirm the result in Chrome DevTools, Application panel, which shows manifest errors and the active service worker.

Mistakes To Avoid

• Shipping one icon and letting browsers scale it.
• Caching API responses for speed and forgetting they change.
• Pointing start_url outside the scope, which browsers silently ignore.
• Assuming iPhone installs behave like Android. Test on both.

Limits

Everything here is read from public files, so the check works on any site, including competitors and prospects. The registration check reads page HTML and inline scripts. Apps that register the worker inside a bundled file will show no registration here even when one exists; DevTools is the confirmation. The checker does not download icons to confirm their pixel sizes.

For Agencies

An installable app is a strong upgrade for clients whose customers return often: booking, ordering, field crews and members. Wise Media checks these rules on every web app it ships, and a readiness report like this is a clear way to scope that work.