Glossary · Networking

HTTP Status Code

An HTTP status code is the three-digit number in a server response that tells the client whether a request succeeded, was redirected or failed, and why.

Updated October 5, 2026

An HTTP status code is a three-digit number in the first line of every HTTP response, such as HTTP/1.1 404 Not Found. The first digit gives the class, and the rest identifies the specific result.

Why it matters

Status codes are how browsers, search engines, APIs and monitors decide what happened. A wrong code causes real damage: a deleted page returning 200 creates "soft 404" problems, and a temporary error returning 404 can make crawlers drop a page. Monitors depend on codes to tell up from down.

Example

ClassMeaningExamples
1xxInformational100 Continue, 101 Switching Protocols
2xxSuccess200 OK, 201 Created, 204 No Content
3xxRedirection301, 302, 304 Not Modified, 308
4xxClient error400, 401, 403, 404, 410, 429
5xxServer error500, 502, 503, 504
curl -sI https://example.com/missing | head -n 1
# HTTP/2 404

Common mistakes

  • Returning 200 OK with an error page in the body, which hides failures from monitors and search engines.
  • Using 302 where a permanent 301 is intended, or the reverse.
  • Treating all 5xx as the same. 502, 503 and 504 point to different layers.
  • Mixing up 401 (not authenticated) and 403 (authenticated but not allowed).

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