HTTP Status Code Reference
HTTP status codes are three-digit responses a server sends after each request. They're grouped into five classes: 1xx informational, 2xx success, 3xx redirection, 4xx client error, and 5xx server error. The meanings below follow RFC 9110 (standards) with common unofficial extensions noted separately.
Most Common Codes Developers Meet
200 OK — the request succeeded. 301 Moved Permanently — the URL has permanently moved (use in redirects for SEO). 404 Not Found — the resource doesn't exist. 401 Unauthorized — authentication required. 403 Forbidden — no permission. 429 Too Many Requests — rate-limited. 500 Internal Server Error — something broke on the server.
HTTP Status Codes FAQ
What does the first digit tell me? 1=info, 2=success, 3=redirect, 4=your client's fault, 5=server's fault. Which is better for redirects: 301 or 302? 301 is permanent (SEO passes link equity), 302 is temporary. What's an unofficial code? Codes like 418 I'm a Teapot are fun extensions that aren't part of the RFC — use them for internal tools, not public APIs.