Answer

Do PWAs support background sync?

Short answer

Partially. Chromium browsers (Chrome, Edge, Android WebView, Samsung Internet) support the Background Sync API for retrying failed requests, and Periodic Background Sync for scheduled updates. iOS Safari and Firefox do not support either. Fall back to Push notifications for cross-platform re-engagement.

By InstantPWA engineering·Reviewed July 22, 2026

One-shot Background Sync

Register a sync tag when a request fails. The browser retries it once connectivity returns, even if the tab is closed. Widely supported on Chromium.

Periodic Background Sync

Runs a task at roughly daily intervals. Chrome only, requires a "high site engagement" score, and users can disable it in browser settings.

The iOS workaround

iOS Safari does not implement either API. Use silent Web Push (via Notification.showNotification with silent: false is required) to wake the SW and refresh caches.

Sources

Can a PWA send push notifications on iOS?

Yes. Since iOS 16.4 (March 2023), a PWA can send Web Push notifications on iPhone and iPad — but only after the user installs it to the home screen. Push in a regular Safari tab is not supported, and the user must explicitly grant notification permission from inside the installed PWA.

Do PWAs work offline?

PWAs can work offline, but only for content their service worker has explicitly cached. Registering a service worker does not automatically make a site offline-capable — you decide what to cache (app shell, API responses, images) and what strategy to use (cache-first, network-first, stale-while-revalidate).