What Are Service Workers and Their Offline Leftovers

What a service worker actually does

When a site registers a service worker, the browser starts running its script in the background, separate from any tab. The worker intercepts the site's network requests, serves files from local cache, renews itself from the network, and keeps listening for push notifications even after you close every window. That is the machinery behind installable web apps, offline web mail and messengers that work without a store app.

It is a genuinely good design — and a storage design with no sense of shame. A browser lets an origin keep gigabytes in its CacheStorage if the disk can spare it, and a web player or a document editor you opened once can hold hundreds of megabytes for years. The worker and its caches sit inside your browser profile, and nothing evicts them unless storage pressure forces the browser's hand.

Where the leftovers live

In Chrome and other Chromium browsers the storage sits inside each profile folder, under Service Worker\CacheStorage and Service Worker\ScriptCache. The usual suspects are predictable: web mail, web players of every streaming service, browser-based messengers, and office suites that cache their entire interface for offline work. Firefox keeps the same idea in its own storage directories, keyed per origin, so the leftovers are not even a Chromium-only habit.

• Chrome/Edge: %LOCALAPPDATA%\<browser>\User Data\<profile>\Service Worker\CacheStorage — gigabytes are normal here
• Heaviest origins: web mail, streaming web players, browser messengers, online office suites
• The storage persists across browser restarts, updates and reboots by design
• Per-site size is visible in DevTools → Application → Storage, or in chrome://settings/content/all
• A site you visited once keeps its cache until you clear it — there is no automatic expiry

Clearing them out safely

For a single site, DevTools → Application → Service Workers has an Unregister button, and chrome://serviceworker-internals lists every registered worker on the profile with the same option. Clearing a site's data from chrome://settings/content/all removes the worker, its caches and its cookies in one sweep — you will be signed out, and the site re-registers on your next visit anyway. Neither action is dangerous: the worst case is that a web app re-downloads its files next time.

For a whole-profile cleanup, hunting folders by hand gets old fast, and Kleaner PRO's Deep Cleaning exists for exactly this job — it sweeps browser caches across profiles in one pass, leftovers like these included. If you would rather stay manual, sort the Service Worker folder by size, delete the heaviest origins, and call it a day. Either way, the space comes back immediately, and the sites rebuild what they need on the next visit.

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