Cache coherence

What CacheStorage exposes and what it cannot prove

CacheStorage is script-visible storage controlled by applications, often through a service worker. It is not the browser HTTP cache, and it does not reveal what a CDN edge currently serves. This check reads only the number of cache namespaces and generic per-cache request counts for the current origin. It does not read response bodies, request URLs, Cache-Control headers, origin addresses or cache names into the report. A zero count does not establish no caching; the browser HTTP cache can still contain resources.

Observe service-worker control independently

A service worker registration is not necessarily controlling the current page. The tool records whether a controller is present and the number of same-origin service-worker registrations, without copying scope or script URLs. An old worker or cached asset might still exist, and version transitions, activation, waiting workers and offline replay require controlled application-specific testing. Read-only observation does not unregister, update or claim ownership of any service worker.

Use user-supplied release markers for a bounded comparison

If you operate an application that exposes explicit release identifiers, supply the versions independently recorded for the loaded browser shell, service-worker release and edge deployment. Two or three provided markers are compared locally. The tool reports only the number of equal and different pairs; no marker values are exported. An equality result is user-supplied consistency, not independently verified cache coherence. A difference is a useful discrepancy to investigate, not proof which layer is stale.

Bound results and preserve uncertainty

This tool inspects at most eight CacheStorage namespaces and accepts at most 2048 observed requests per cache and 4096 overall, within a three-second deadline. Larger or unreadable inventories are marked partial or blocked, rather than silently reporting a false total. The browser may refuse cache enumeration, worker registration APIs may be unavailable, and the cache may change while being observed. The tool does not start a fetch, set cache headers or force revalidation. Under a concurrent cache-deletion race, CacheStorage.open can recreate a namespace even after an existence check, so do not run this inspector during cache maintenance.

Compare with existing deployment and timing evidence

Asset Integrity already checks this platform’s static delivery against its generated build manifest using signed responses and SHA-256. Resource Waterfall explains browser-exposed request timings. Cache Coherence deliberately reuses those existing tools rather than creating a second asset checker or asserting that timing zeros prove cache hits. For a verified edge-versus-origin comparison, an explicitly authorised multi-region gateway and controlled test environment would be required; this phase does not implement it.

Privacy, explicit execution and reporting

Nothing runs until the user presses Inspect browser caches or Compare supplied markers. The browser-only runtime inherits the site’s local-tool CSP, blocking network connections. The tool never clears a cache, mutates storage, registers a worker, contacts a remote target or sends telemetry. Counts and comparison classifications remain in page memory unless deliberately exported as JSON. Clear, reload and page exit remove displayed results. This phase provides diagnostic evidence, not a cache freshness score, security certificate or production change.

Method references and related tools

MDN CacheStorage documents script-visible caches. ServiceWorker controller documents the controlling-worker API. HTTP caching is a separate browser and intermediary mechanism. No live CDN probe is performed.

Asset integrity · All tools · Overall measurement methodology