HTTP Status Codes - yibinericxia/documents GitHub Wiki

100: Continue (everything so far is OK and the client should continue with the request or ignore if if finished)
101: Switching Protocols (for example upgraded to websocket specified in the request header, as well as in the response header)

200: OK
201: Created (for POST method which has created resource successfully)
202: Accepted (return with information to check the status of asynchronous task/batch processing)
204: No Content (the server has fulfilled the request successfully with no entity returned)

301: Moved Permanently (for GET / HEAD permanent redirect)
302: Found (temporary redirect by server to prevent search engine from updating the address, good for the method GET/HEAD)
304: Not modified (may need to clear the browser/DNS cache data, or disable browser extensions)
307: Temporary Redirect (by browser to preserve the method like POST)

400: Bad Request
401: Unauthorized (for invalid user credentials)
403: Forbidden (for user lack of privileges to access the resource)
404: Not Found (for non-existing resource, or no permission to resource for security)
405: Method Not Allowed (the method is not supported although the server knows the request, such as PUT instead of POST)
406: Not Acceptable (for request with unsupported content negotiation defined in header of Accept, Accept-Encoding or Accept-Language)
408: Request Timeout (it indicates network latency due to slow-connection/heavy-traffic at client side or server being too busy with misconfiguration at server side)
409: Conflict (for a conflict in the request with the current state of the resource)
413: Request Entity Too Large (when payload size exceeds the server file size limit)
415: Unsupported Media Type (for request with unsupported format defined in header of Content-Type or Content-Encoding)
417: Expectation Failed (for the server cannot meet the expectation set in HTTP request header Expect, for example, Expect: 100-continue with too large file)
422: Unprocessable Entity (the server understands the content type (see 415), and the syntax of the request entity (see 400), but was unable to process the contained body)
499: Client Closed Request (the connection closed by the client, such as browser or proxy, before the server delivers response, might due to client side timeout)

500: Internal Server Error
502: Bad Gateway
503: Service Unavailable (server might be down or overloaded)
504: Gateway Timeout (it indicates the gateway/proxy did not receive timely response due to heavy traffic from upstream server thus could not complete the request)