HTTP Status Code Reference

HTTP Status Code Classes Explained

HTTP status codes are three-digit integers returned by a server in response to a client request. The first digit defines the class of response; the remaining two digits provide further detail within that class.

1xx — Informational

Provisional responses indicating the request was received and the server is continuing to process it. The client should be prepared to receive a final response after the informational one. The most common, 100 Continue, is used with large request bodies: the client sends headers first and only sends the body after receiving 100.

2xx — Success

The request was successfully received, understood, and accepted. 200 OK is the default for most successful requests. 201 Created should be used when a new resource was created — include a Location header pointing to it. 204 No Content is correct for DELETE and PATCH responses that return no body.

3xx — Redirection

Further action is needed to complete the request. Always send a Location header with the target URL. Use 301 for permanent moves (SEO transfers link equity), 307/308 when you need to preserve the HTTP method (unlike 301/302, which browsers may convert to GET).

4xx — Client Errors

The request contains bad syntax or cannot be fulfilled by the server. The client should not repeat the request without modification. A frequent source of confusion: 401 means "not authenticated" (provide credentials), while 403 means "authenticated but not authorized" (access denied regardless of credentials).

5xx — Server Errors

The server failed to fulfil an apparently valid request. These indicate problems on the server side. 500 is the generic error; 502/503/504 are common in proxy/load-balancer setups. When returning 5xx, include a Retry-After header whenever possible to help clients back off gracefully.