1xx Informational Details
100 Continue An interim response - the client may continue with its request.
101 Switching Protocols Server is complying with client request (via Upgrade message header field) to change the connection's application protocol.
2xx Successful Details
200 OK The request has succeeded.
201 Created Fulfilled request has resulted in a new resource being created (specified in the Location header field).
202 Accepted The request has been accepted for processing, but the processing is incomplete.
203 Non-Authoritative Information The information returned in the entity header is from a third-party or local copy, not the original server.
204 No Content Request has been fulfilled, but there is no new information returned. Client document view does not change.
205 Reset Content Request has been fulfilled, and the client should update its document view.
206 Partial Content Server is returning partial data in response to a GET request. The request included a Range header field indicating the desired range.
3xx Redirection Details
300 Multiple Choices The requested resource is any one of a set of resources.
301 Moved Permanently The requested resource has a new URI, and any future references to the resource should be done using one of the returned URIs.
302 Moved Temporarily The requested resource exists temporarily under a different URI, and the client should continue to use the requested URI to access this resource.
303 See Other The requested resource exists at a different URI and should be retrieved by issuing a GET to that location.
304 Not Modified Returned when the client has issued a conditional GET, and the document has not been modified.
305 Use Proxy The requested resource must be accessed via the proxy listed in the Location field.
4xx Client Error Details
400 Bad Request Server received a syntax error in the client's request.
401 Not Authorized The request requires user authentication. The response must contain a WWW-Authenticate header containing a challenge applicable to the resource requested.
402 Payment Required Reserved for future use.
403 Forbidden The server understood the request and refuses to fulfill it. The request should not be repeated. Authorization is irrelevant.
404 Not Found The resource at the requested URI does not exist.
405 Method Not Allowed The method used by the client is not allowed for the resource requested.
406 Not Acceptable The resource requested is in a format that is unacceptable with regards to the format requested by the client.
407 Proxy Authentication Required The client must first authenticate with the proxy. The proxy must return a Proxy-Authenticate header field.
408 Request Timeout The client did not provide a request within the time period that the server was prepared to wait.
409 Conflict The request could not be completed due to a conflict with the current state of the resource.
410 Gone The requested resource no longer exists on the server, and no forwarding address is known. Should be considered permanent.
411 Length Required The server refuses to accept the request without a defined Content-Length.
412 Precondition Failed The precondition specified in at least one request-header field failed when tested on the server.
413 Request Entity Too Large The server is refusing the request because the request entity is larger than the server is willing or able to process.
414 Request-URI Too Long The server is refusing the request because the Request-URI is longer than the server is willing to interpret.
415 Unsupported Media Type Request refused because the entity of the request is in a format that is unsupported by the requested resource for the requested method.
5xx Server Error Details
500 Internal Server Error The server encountered an unexpected condition which prevented it from fulfilling the request.
501 Not Implemented The server does not support the functionality required to fulfill the request.
502 Bad Gateway The server, in the role of a gateway or proxy, received an invalid response from the upstream server while attempting to fulfill the request.
503 Service Unavailable The server is temporarily unable to service the request, but is should be able to in the future.
504 Gateway Timeout The server, in the role of a gateway or proxy, did not receive a timely response from the upstream server while attempting to fulfill the request.
505 HTTP Version Not Supported The server does not support, or refuses to support, the HTTP protocol version that was requested.

Adapted from RFC 2068