404 error (Not Found)

The 404 error (Not Found) is an HTTP status code returned when the server is working correctly but no resource exists at the requested URL. It is the most recognizable error on the web — every user has met it and every large site produces it — so the goal is not to eliminate 404s entirely but to manage them deliberately.

How the 404 error works

Typical sources include pages deleted without a redirect, URL structures changed during a migration or redesign, typos in internal or external links, and misconfigured application routing. A separate phenomenon is the soft 404: a "page not found" message served with status 200, which confuses search engine crawlers into indexing an empty page instead of registering that the resource is gone. A correctly configured server returns a genuine 404 for missing addresses — or 410 when content has been removed permanently, signaling crawlers not to return.

Practical applications

Good 404 management has three pillars. First, a helpful error page: navigation, a search box and links to key sections keep the visitor on the site instead of bouncing. Second, monitoring: the indexing report in Google Search Console and the server logs reveal which missing URLs receive traffic and where the links come from. Third, remediation: broken internal links get fixed at the source, while removed pages with valuable backlinks are pointed via a 301 redirect to the closest relevant page. Keeping the XML sitemap current stops crawlers from revisiting long-deleted addresses. At scale, unmanaged 404s waste crawl budget and leak link equity — but the occasional one is simply part of a living website.