HTTP Status Code Reference
Free HTTP status code reference. Search every common status code from 1xx to 5xx with a plain-English explanation.
How HTTP status codes are organized
Every HTTP response starts with a three-digit status code, and the first digit tells you the general category before you even read the rest: 1xx means the request was received and processing continues, 2xx means it succeeded, 3xx means further action (usually following a redirect) is needed, 4xx means the client's request was somehow wrong, and 5xx means the server failed to fulfil an otherwise valid request.
Frequently asked questions
What is the difference between a 401 and a 403 status code?
401 Unauthorized means the request has no valid authentication credentials — you need to log in or provide a valid token. 403 Forbidden means the server understood who you are but you don't have permission to access that resource, regardless of authentication.
What does a 502 vs a 504 error mean?
502 Bad Gateway means a server acting as a proxy or gateway got an invalid response from an upstream server. 504 Gateway Timeout means that upstream server simply didn't respond in time. Both usually point to a problem with a backend service rather than the site itself.
Why do I see 301 and 302 for the same redirect?
301 Moved Permanently tells browsers and search engines the resource has permanently moved, so they should update bookmarks and search indexes to the new URL. 302 Found is a temporary redirect — the original URL should still be treated as the canonical one.
What does 404 vs 410 mean for a missing page?
404 Not Found means the server can't find the requested resource, with no indication of whether it ever existed. 410 Gone is a deliberate statement that the resource used to exist but has been permanently removed — some crawlers treat it as a stronger signal to drop the page from their index sooner.