No 404 page
Part of Documentation, UX & Accessibility, which counts for 15% of the overall score. When this check fires it deducts 2 points from that category, once per scan, no matter how many places it turns up.
What it detects
No not-found page or catch-all route was found, so unmatched URLs likely show a raw error instead of a friendly page.
Why it matters
Without a dedicated not-found page, a mistyped URL or a stale link lands users on a framework default or a raw error, with no way back into your app. It reads as broken even when nothing is wrong. A small branded 404 with a link home turns a dead end into a one-click recovery.
How to fix it
Add the catch-all your framework expects. Next.js App Router: create app/not-found.tsx (pages router: pages/404.tsx). React Router: add <Route path="*" element={<NotFound />} /> as the last route. Express: add a final app.use((req, res) => res.status(404).render or send) after all other routes. Keep the page simple: a short message, the site header or logo, and a link back to the home page, and make sure it actually returns HTTP status 404.
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