What icon sizes does a PWA need?

A Web App Manifest is a JSON file — usually manifest.webmanifest — that declares your app’s name, icons, start URL, theme colour and display mode. Browsers read it to decide whether to offer the install prompt and what icon and name to show on the home screen.

On Android, Chromium automatically generates a splash screen for an installed PWA using the manifest’s name, background_color, theme_color and the largest available icon — you do not draw it manually. It appears briefly while the app’s first paint loads after the user taps the icon. iOS Safari does not generate one automatically and requires custom <link rel="apple-touch-startup-image"> tags per device size.

Yes, a PWA needs HTTPS. Browsers refuse to register a service worker on a plain HTTP origin because it can intercept and modify every network request, which would be a serious security risk over an unencrypted connection. The only exception is localhost and 127.0.0.1, which browsers treat as a secure context for local development.

A service worker moves through four stages: install (fired once when the browser first downloads a new or changed worker), waiting (if an old version still controls open tabs), activate (once it takes control, typically after all old tabs close or skipWaiting() is called) and idle, where the browser terminates it between events to save memory.

Browsers automatically check your service-worker script for byte-level changes on every navigation (and roughly every 24 hours in the background). If it differs, the new version installs and waits until old tabs close before activating. Calling self.skipWaiting() in install and clients.claim() in activate makes the new version take over immediately instead of waiting.