What is a PWA?

PWA: an implementation acronym, not a product category

PWA abbreviates Progressive Web App, but in engineering standups it means something more concrete than a vision statement: a checklist of shippable artifacts—manifest.webmanifest, sw.js, HTTPS, icons—that unlock install prompts in Chrome, Edge, and Samsung Internet.

This entry covers the acronym from an audit and implementation angle: which files to create, how to register them, what Lighthouse inspects, and where teams break SEO while chasing the install badge. For the strategic “what capabilities does a Progressive Web App unlock?” narrative, see the Progressive Web App glossary page.

Minimum viable PWA stack

Missing any installability pillar blocks “Add to Home Screen” on most platforms.

Web app manifest field reference

{
  "name": "Crawlox Site Audit",
  "short_name": "Crawlox",
  "start_url": "/?utm_source=pwa",
  "display": "standalone",
  "background_color": "#ffffff",
  "theme_color": "#0f172a",
  "icons": [
    { "src": "/icons/icon-192.png", "sizes": "192x192", "type": "image/png" },
    { "src": "/icons/icon-512.png", "sizes": "512x512", "type": "image/png", "purpose": "any maskable" }
  ]
}

SEO-relevant notes:

• name / short_name affect install UI—not Google titles. Keep <title> tags authoritative for search snippets.
• start_url should resolve to indexable content or redirect to it; avoid noindex on default launch URL.
• scope limits which paths the installed app controls—mis-scoping can trap users off crawlable sections.

Service worker registration checklist

if ('serviceWorker' in navigator) {
  window.addEventListener('load', () => {
    navigator.serviceWorker.register('/sw.js');
  });
}

Inside sw.js, define fetch strategy explicitly:

Never return offline.html for navigation requests without attempting network—crawlers do not execute your retry UI.

Lighthouse PWA audit mapping

Chrome Lighthouse “Installable” category roughly maps to:

1. Served over HTTPS.
2. Registers a service worker controlling page and start_url.
3. Manifest includes name, icons, start_url, display, theme_color.
4. start_url responds 200 when offline (after precache)—test carefully for SEO side effects.

Passing audits proves technical installability—not business readiness. Ship only after HTML parity tests pass.

Pre-deploy verification script (conceptual)

□ manifest validates in Web App Manifest validator
□ service worker activates without console errors
□ curl -A Googlebot homepage → full HTML body (not offline shell)
□ start_url matches canonical preference
□ icons exist and return 200
□ theme-color matches brand (UX, not SEO)
□ Cache-Control on HTML ≠ immutable long-term cache

Automate manifest JSON schema tests in CI.

Framework shortcuts

Generated workers still need human review of navigation route rules.

PWA implementation mistakes that hurt SEO

1. App shell only in cache — /blog/post-1 serves empty #app offline.
2. Skipping SSR on marketing routes — installable but invisible to search.
3. Canonical drift — start_url query params indexed separately; use consistent canonical tags.
4. Blocking robots on sw.js — unnecessary; allow fetch so browsers install correctly.
5. Long max-age on HTML at CDN — stale meta tags after deploy; pair with Cache-Control discipline.

PWA vs native wrapper (SEO clarity)

Capacitor and Cordova wrap WebViews—the indexed web URLs remain your SEO surface. Store listings are separate. Do not noindex the web app because a native build exists.

Acronym disambiguation

Maintenance cadence

• Bump CACHE_VERSION in sw.js on deploy; purge old precaches.
• Re-run Lighthouse after manifest icon changes.
• Monitor Search Console indexed pages after worker strategy changes.
• Document which routes are network-first in runbooks.

How Crawlox helps with PWA implementation audits

Crawlox requests pages without service worker interception—mirroring crawler behavior. After PWA rollout, compare Crawlox HTML snapshots to browser DevTools with worker disabled. Mismatches reveal worker strategies serving incomplete documents to bots. Fix network-first rules for HTML before chasing Lighthouse install badges.