HTTP Status Codes List & Lookup

Every HTTP response starts with a three-digit status code that tells the browser, an API client or a search engine what happened. This lookup covers the full IANA registry — the codes defined in RFC 9110 and the WebDAV and later RFCs — plus the unofficial codes you meet in nginx logs and on Cloudflare error pages, each with a plain explanation, the usual cause and what to do about it.

How to use this tool

1. Type a code such as 502, or a word such as redirect, timeout or cookie.
2. Narrow the list by class if you like, for example only 5xx server errors.
3. Read the meaning, the typical fix, whether the response is cacheable by default and the RFC section that defines it.
4. Leave the box empty to browse the full table.

Formula

class = first digit: 1 informational · 2 successful · 3 redirection · 4 client error · 5 server error

RFC 9110 requires clients to understand the class of any code and to treat an unknown code like the x00 code of its class, so an unrecognised 299 is handled as 200 and 477 as 400. Responses with 200, 203, 204, 206, 300, 301, 308, 404, 405, 410, 414 and 501 may be cached without explicit freshness headers (heuristic caching).

Example

Searching 504 shows Gateway Timeout from RFC 9110 §15.6.5: a proxy such as nginx or a load balancer gave up waiting for the application behind it, so the fix is on the server — speed up the slow request or raise the proxy timeout. Searching 524 shows the Cloudflare version of the same problem, with Cloudflare's default 100-second limit.