Page not found page

Problem Context

• Users may arrive from bookmarks, search results, letters, email links, notifications, copied addresses, external referrals, or stale in-product links.
• The missing route may be a public content page, service step, deleted object, expired signed link, renamed resource, or protected object that must not disclose existence.
• The service itself may be healthy, so outage, spinner, or local component error treatment would misrepresent the condition.
• The organization needs operational evidence to find broken links, redirect removed pages, retire stale communications, and improve search recovery.

Selection Rules

• Choose page not found page when the requested route, page, file, object URL, or deep link does not resolve to a valid destination.
• Use typed or pasted address guidance when users may have entered an incorrect or incomplete URL.
• Use moved or removed page guidance when the product knows the old page has a replacement, archive, topic page, or support route.
• Use signed-in dashboard recovery when a deep link expired or an account-scoped task moved to another current state.
• Use neutral no-disclosure copy for protected resources when the product must not reveal whether a private object exists.
• Provide search only when it is available and likely to recover the missing content; otherwise route to a start page, dashboard, sitemap, contact page, or support queue.
• Offer report-broken-link or contact paths when broken internal links, letters, forms, or external references may need correction.
• Use service unavailable page when the valid service route exists but cannot currently handle requests.
• Use error state when a valid page or section failed after loading enough context for in-place recovery.
• Use empty state when the requested page is valid and loaded successfully but the resulting collection contains no objects.

Required States

• Unknown route from typed or pasted URL.
• Broken in-product link.
• Removed public page with a replacement or closest topic route.
• Expired deep link that routes signed-in users to a dashboard or current task list.
• Private or policy-masked resource that uses no-disclosure copy.
• Search recovery state with query entry and useful suggestions.
• Report broken link or contact support state.
• Popular or common task links state for broad public pages.
• Localized or service-scoped not-found page.
• Logged 404 state with missing path, referrer, and safe diagnostic identifier.

Interaction Contract

• The page loads as a stable destination instead of redirecting users without explanation.
• The page title, H1, visible copy, HTTP status, and analytics all agree that the requested resource was not found.
• Recovery links lead to valid destinations and are labeled by destination rather than vague escape words.
• Search, if present, accepts keyboard input, submits reliably, and preserves the user's query.
• Private-resource variants avoid disclosing names, owners, counts, or IDs beyond what the user's role is allowed to know.
• The missing path and referrer are captured for diagnostics without exposing sensitive values in the visible UI.

Implementation Checklist

• Configure the route, edge, or server to return a real 404 status for unresolved public URLs.
• Use a page title that includes Page not found and the service or site name.
• Write concise no-blame copy that explains likely address, copied-link, moved-page, or removed-page causes.
• Add search, start-page, dashboard, contact, report-broken-link, replacement-page, or popular-task links according to the product context.
• Keep header and footer navigation when they help orientation, but remove breadcrumbs that imply a valid parent trail for the missing page.
• Avoid technical jargon, humor that obscures the condition, warning colors as the only signal, and raw routing errors.
• Track missing URL, referrer, account state, locale, and recovery link usage so teams can repair broken links and redirects.
• Test external links, bookmarks, old route redirects, unauthenticated and authenticated deep links, protected resources, screen readers, keyboard navigation, zoom, and mobile widths.

Common Generated-UI Mistakes

• Returning a successful status with page-not-found copy.
• Automatically redirecting to the homepage without explaining that the requested page was not found.
• Using page not found for a service outage, form validation problem, submission failure, loading delay, or empty collection.
• Showing only a code, stack trace, route matcher name, or framework error.
• Providing no search, start, dashboard, contact, replacement, or report-broken-link route.
• Revealing private object names or owners in a no-disclosure context.
• Leaving old letters, emails, help pages, and in-product links pointed at missing URLs.

Critique Questions

• Can users tell that the URL did not resolve while the service may still be reachable?
• Does the page give recovery paths that match how this user arrived?
• Is the missing path safe to show, or would it disclose a protected object?
• Are broken links and recovery actions measurable for repair?
• Would this situation be more accurately handled by service unavailable page, error state, empty state, permission denied state, or redirect?