What are HTTP status codes?
HTTP status codes are three-digit numbers returned by a web server in response to every HTTP request. They tell the client whether a request succeeded, failed, or requires further action. Status codes are grouped into five classes by their first digit.
Frequently asked questions
What is the difference between 401 Unauthorized and 403 Forbidden?
401 means the client is not authenticated — no valid credentials were provided. The client should authenticate first. 403 means the server knows who the client is but refuses access — authentication would not help.
What is the difference between 301 and 302 redirects?
301 Moved Permanently is a permanent redirect — search engines transfer link equity to the new URL. 302 Found is temporary — the original URL stays canonical and search engines do not transfer PageRank.
What does 429 Too Many Requests mean?
The client has exceeded the server's rate limit. The server may include a Retry-After header. Back off and retry after the indicated time.
What is 418 I'm a Teapot?
An April Fools' joke from RFC 2324 (Hyper Text Coffee Pot Control Protocol, 1998). A server that is a teapot may refuse to brew coffee with this code. It has been retained in the spec as an Easter egg.
What is the difference between 500 and 502?
500 Internal Server Error means the origin server itself encountered an error. 502 Bad Gateway means a proxy or gateway (e.g. Nginx, a CDN) received an invalid response from the upstream server it was trying to reach.
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