Pwa Offline Readiness Review

PWA Offline Readiness Review

Purpose

A manifest.json that passes JSON-schema validation, and a Lighthouse PWA badge that reads 100, both prove far less than they appear to. The W3C manifest spec, beforeinstallprompt behavior, and offline-fallback rendering are three separate systems that must each work — a pass on one says nothing about the other two. The common failure mode is "checklist theater": a team ships a schema-valid manifest and a registered service worker, calls the app a PWA, and only discovers in production that the install banner never fires (display: browser left at a framework default) or that a network drop shows the browser's stock offline error page instead of a designed fallback. This skill performs the end-to-end verification — install criteria against the live origin, service-worker activation state, and an actual offline-throttle navigation test — that a static manifest read cannot substitute for.

When to use

Use this skill when the user asks to:

• audit whether an app is a "real" installable PWA, not just manifest-schema-valid,
• debug why the install prompt / beforeinstallprompt never fires despite a Lighthouse PWA pass,
• review offline-fallback behavior, or debug a network drop showing the browser's default error page instead of a designed offline page,
• validate manifest fields (name, icons, start_url, scope, display) against W3C installability criteria before a release.

When not to use

• Caching-strategy correctness for an already-installable app (route classification, CacheFirst vs. NetworkFirst, authenticated-response caching risk) — hand off to service-worker-cache-strategy-review; that skill owns caching-strategy depth and this one does not duplicate it.
• General HTTP Cache-Control/CDN caching review with no manifest or service-worker installability question involved.

Context7 Documentation Protocol

Manifest-injection defaults, precache-manifest generation, and offline-fallback wiring differ by framework PWA plugin and by version — never assert a gap is "the app's fault" without checking the plugin's current documented default first.

1. Call ToolSearch with query "context7" (or "select:mcp__Context7__resolve-library-id,mcp__Context7__query-docs") to load the Context7 tools if not already loaded in this session.
2. Always ground manifest-field and installability-criteria claims against the W3C manifest spec directly (official_docs), not a vendor summary of it — vendor blog posts routinely lag or simplify the spec's display/purpose/icon-size language.
3. If the project uses vite-plugin-pwa, resolve /websites/vite-pwa-org_netlify_app and query its manifest-generation, generateSW/injectManifest, and precache globPatterns/maximumFileSizeToCacheInBytes behavior before asserting an asset or route is missing from precache "because the app didn't configure it" — the plugin has documented defaults and size ceilings that silently exclude assets.
4. If the project uses next-pwa (@ducanh2912/next-pwa), resolve /ducanhgh/next-pwa and query its fallbacks config (document/data/image/audio/video/font) and default-offline-page conventions (pages/_offline.tsx / app/~offline/page.tsx) before concluding a fallback route is absent — the plugin auto-wires a default path if the file exists at the conventional location.
5. If the underlying precaching/fallback mechanism is hand-rolled Workbox (not a framework plugin), resolve /googlechrome/workbox and query offlineFallback/setCatchHandler/precacheAndRoute semantics — confirm whether the fallback handler checks the precache before an offline-fallbacks cache, since a bug in that check order is a common cause of the fallback silently failing.
6. Query for the exact behavior in question per review, not from memory of a prior session — plugin defaults and Workbox recipe internals change across major versions.
7. If Context7 is unavailable or has no relevant match, fall back to official_docs / the bundled references, and mark the claim documentation-based (Context7 unavailable) rather than presenting it as freshly verified.
8. Never invent a manifest field, plugin config key, or Workbox API that no queried source confirms.

Lean operating rules

• Verify HTTPS on the actual target origin first — the W3C-implementing browsers refuse installability outright without it (localhost is the only common documented exception); if HTTPS is not confirmed, stop there, because every downstream installability check is moot until it is fixed.
• Treat display: browser as a deliberate product choice to surface and confirm with the user, not a silent bug to "fix" — it is valid per spec, but it disqualifies the install-prompt flow by design, and teams frequently leave it at a framework default without realizing the consequence.
• Do not declare an app "installable" from manifest JSON validity alone — confirm HTTPS, a service worker that reaches the activate state, and a qualifying display value together; each is independently necessary and none is sufficient alone.
• Do not declare an app "offline-ready" from precache-manifest file lists or service-worker registration code alone — perform an actual DevTools offline-throttle navigation to a previously unvisited route and observe what renders; precaching and route-matching are separate concerns, and a precached fallback page with an unmatched route still fails offline.
• Confirm the offline-fallback page is itself guaranteed precached, including its own dependencies (fonts, inline API calls, images) — a fallback page that depends on an uncached asset fails to render exactly when it is needed.
• Treat the Lighthouse PWA category score as a secondary, corroborating signal only — it can pass on stale audit state and does not reproduce the live beforeinstallprompt browser signal; require the manual browser-session listener test as the primary proof of installability.
• Flag any start_url, icon, or fallback-asset reference pointing to an HTTP origin or an unpinned third-party CDN — a mixed-content or unverifiable icon source undermines both installability and the fallback page's guarantee of availability.
• Never recommend caching user-specific or authenticated content inside the offline-fallback route — it must render identically and safely for any unauthenticated network-offline visitor; if the app's fallback design leaks account state, that is a blocker, not a caching-strategy nuance for the sibling skill to solve.
• Label every claim as live evidence, spec-cited, documentation-based, or inference so the reviewer knows what was actually tested versus reasoned about from file contents.

References

Load these only when needed:

• W3C manifest installability checklist — use when validating manifest field-by-field against W3C installability criteria (name/short_name, icons, start_url/scope, display) and when diagnosing a missing install prompt.
• Offline fallback precache patterns — use when reviewing how the offline-fallback route is registered and precached, across hand-rolled Workbox, vite-plugin-pwa, and next-pwa conventions.
• Live installability and offline verification protocol — use for the step-by-step manual test procedure (HTTPS check, service-worker activation, beforeinstallprompt listener, DevTools offline-throttle navigation) and for interpreting Lighthouse-vs-live divergence.

Response minimum

Return, at minimum:

• pass/fail verdict per W3C installability field (HTTPS, name/short_name, icons, start_url/scope, display), each labeled with its evidence level,
• service-worker registration and activation status (not just "registered" — confirm activate was reached),
• the actual (not inferred) offline-navigation test result for at least one previously unvisited route, and the offline-fallback page's precache/dependency-precache status,
• explicit note on whether display disqualifies install prompts by design and whether that was confirmed as intentional with the user,
• a handoff note to service-worker-cache-strategy-review if the gap identified is a caching-strategy implementation detail rather than an installability/offline-navigation gap.