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Error Pages

Explore offline screens, HTTP errors, and application failures.

Error playground

Choose a state to compare its message, meaning, and recovery action.

Preview · 404

Page not found

Check the address or return to a known page.

What happened?
The resource was not found, or the server will not disclose it.

These are simulated interfaces. Selecting a code does not change this page’s HTTP response.

This site’s offline page

The actual standalone fallback, displayed here while you are online.

The service worker serves this fallback when a same-origin page navigation fails to reach the network. It needs an installed, controlling service worker; opening this preview does not enable offline mode.

Open offline page

This site’s 404 page

A missing address displays the existing Page not found interface.

This static preview disables scripts. Back to home opens inside the frame; the scripted Go back control is inactive.

Which kind of failure?

  • Offline: the browser cannot reach the network. There may be no server response at all.
  • 4xx: the request needs attention, such as an incorrect address, missing authentication, or a rate limit.
  • 5xx: the server or an upstream service failed to fulfill the request. A 500 is a general server error; 505 specifically concerns the HTTP version.
  • Application crash: rendering can fail after a page has loaded successfully. This site’s global error boundary offers Try again and Back to home, with an error ID when available. The playground illustrates this state without crashing the app.

Maintenance commonly uses 503. An empty list and a loading indicator are ordinary interface states, rather than error pages.

References: MDN HTTP status codes and HTTP Semantics.