HTTP Status Codes Reference

They are three-digit numbers a server returns with every HTTP response to tell the client how the request went. The first digit sets the class: 1xx informational, 2xx success, 3xx redirection, 4xx client error and 5xx server error.

A 4xx code means the problem is on the client side, like a bad URL (404) or missing authentication (401), so changing the request may fix it. A 5xx code means the server failed to handle a valid request, such as a crash (500) or downtime (503), and is usually out of the client's control.

404 Not Found means the resource does not exist at that URL. 301 Moved Permanently means it lives at a new URL for good, so links and search engines should update. 500 Internal Server Error is a generic server-side failure while processing the request.

Every web request returns one. You see them in browser developer tools under the Network tab, in server and access logs, in curl output, and in API responses. Tools like uptime monitors and crawlers act on them too.

200 OK means the request itself succeeded at the HTTP level, but the body can still contain an application error. Well-built APIs use specific codes like 201 Created, 400 Bad Request or 422 Unprocessable Entity to be precise.

Yes. The list follows the IANA HTTP Status Code Registry and the relevant RFCs, covering the standard 1xx through 5xx codes. It does not include vendor-specific extensions used by individual proxies or CDNs.