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What is Periodic Background Sync?

Short answer

Periodic Background Sync lets an installed PWA periodically wake its service worker to refresh cached content — for example, prefetching news articles — even when the app is not open. It requires the periodic-background-sync permission, is only available on installed PWAs, and Chromium decides the actual interval based on site engagement, not the requested minimum.

By InstantPWA engineering·Reviewed July 25, 2026

How it differs from one-off sync

One-off Background Sync retries a single failed request once connectivity returns; Periodic Background Sync runs recurring refresh tasks on a browser-controlled schedule.

Browser support

Chromium-based browsers on desktop and Android only, and only after the PWA is installed; Safari and Firefox do not support it.

Permission model

The browser silently grants or denies the permission based on engagement heuristics (site engagement score) rather than a user-facing prompt.

Sources

Related
What is the Background Sync API?
The Background Sync API lets a service worker register a task that the browser retries automatically once the device is back online, even if the user has closed the tab. It is commonly used so a form submission or message made while offline is not lost — it queues, then fires the moment connectivity returns.
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).
What is the App Badging API?
The Badging API lets an installed PWA set a small numeric badge (or a plain dot) on its home-screen or taskbar icon, mirroring the unread-count badges native apps show. Call navigator.setAppBadge(count) to set it and navigator.clearAppBadge() to remove it — no argument shows a plain dot.
What is the Web Share API?
The Web Share API lets a page call navigator.share({ title, text, url }) to open the operating system’s native share sheet, so users can send a link to Messages, Mail, social apps or any other installed share target — the same experience as sharing from a native app.
What is the Web Share Target API?
The Web Share Target API lets an installed PWA declare a share_target entry in its manifest so it shows up in the device’s share sheet as a destination — the same way Twitter or Google Photos appear when you tap "Share" from another app. The declared URL receives the shared title, text, url or files as a request.