HTTP Status Codes Reference

Search or filter every common HTTP status code. Each response from a web server starts with a three-digit code that says what happened.

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Code	Name	Meaning
100	Continue	The server received the request headers; the client should continue sending the body.
101	Switching Protocols	The server agrees to switch protocols, for example to WebSocket.
103	Early Hints	Lets the browser start preloading resources while the server prepares the full response.
200	OK	The request succeeded. The meaning depends on the method: GET returns data, POST returns the result of the action.
201	Created	A new resource was created. Usually returned by POST or PUT, with a Location header pointing to it.
202	Accepted	The request was accepted for processing but is not finished yet (asynchronous work).
204	No Content	Success, with no body to return. Common for DELETE and for updates that need no response data.
206	Partial Content	Only part of the resource is returned, in answer to a Range request (resuming downloads, video seeking).
301	Moved Permanently	The resource has a new permanent URL. Search engines transfer ranking to the new address.
302	Found	Temporary redirect. The client should keep using the original URL in future.
303	See Other	Redirects to another URL with GET, typically after a form POST.
304	Not Modified	The cached copy is still valid, so no body is sent. Saves bandwidth.
307	Temporary Redirect	Like 302, but the client must repeat the same method and body.
308	Permanent Redirect	Like 301, but the method and body must not change.
400	Bad Request	The server cannot understand the request because of malformed syntax or invalid data.
401	Unauthorized	Authentication is required or has failed. (Despite the name, it is about who you are.)
403	Forbidden	The server understood the request but refuses it. You are known but not allowed.
404	Not Found	The resource does not exist at this URL (or the server hides that it exists).
405	Method Not Allowed	The URL exists but not for this HTTP method. The Allow header lists valid ones.
406	Not Acceptable	The server cannot produce a response matching the Accept headers sent.
408	Request Timeout	The server gave up waiting for the client to finish sending the request.
409	Conflict	The request conflicts with the current state of the resource, such as an edit collision or duplicate.
410	Gone	The resource used to exist and was removed on purpose. Stronger than 404.
411	Length Required	The request needs a Content-Length header.
413	Content Too Large	The request body exceeds what the server will accept.
414	URI Too Long	The URL is longer than the server is willing to process.
415	Unsupported Media Type	The request body format (Content-Type) is not supported.
418	I'm a teapot	An April Fools joke from RFC 2324; some APIs return it for playful refusals.
422	Unprocessable Content	The request is well-formed but contains semantic errors, such as failed validation.
425	Too Early	The server will not risk processing a request that might be replayed.
426	Upgrade Required	The client must switch to a different protocol (e.g. newer TLS).
428	Precondition Required	The server requires the request to be conditional (If-Match) to avoid lost updates.
429	Too Many Requests	Rate limit exceeded. Check the Retry-After header and slow down.
431	Request Header Fields Too Large	The headers (often cookies) are too big.
451	Unavailable For Legal Reasons	Access is blocked because of a legal demand, such as censorship or a court order.
500	Internal Server Error	A generic server-side failure: something unexpected broke. Check the server logs.
501	Not Implemented	The server does not support the functionality needed to fulfil the request.
502	Bad Gateway	A gateway or proxy received an invalid response from the upstream server.
503	Service Unavailable	The server is temporarily overloaded or down for maintenance. Retry later (see Retry-After).
504	Gateway Timeout	A gateway or proxy did not get a timely response from the upstream server.
505	HTTP Version Not Supported	The server does not support the HTTP version used.
507	Insufficient Storage	The server cannot store the representation needed to complete the request.
511	Network Authentication Required	The client must authenticate to gain network access, such as captive portals on public Wi-Fi.

The five classes

1xx - informational: the request is still being processed.
2xx - success: the request worked.
3xx - redirection: look somewhere else.
4xx - client error: the request has a problem (wrong URL, no permission, bad data).
5xx - server error: the server failed on a valid request.

401 vs 403

401 means "I do not know who you are - log in". 403 means "I know who you are and you may not do this". For a resource you want to hide completely, some sites deliberately return 404 instead of 403.

301 vs 302 and SEO

Use 301 (or 308) when a page has moved for good so search engines pass ranking to the new URL; use 302 (or 307) for temporary moves such as maintenance or A/B tests.

Debugging tips

4xx: re-check the URL, method, headers, authentication and request body.
5xx: look at the server logs first; the client usually cannot fix it.
429: slow down and honour the Retry-After header; add exponential backoff.
502/504: the problem is between a proxy and the app behind it - check that the app is running and not timing out.