Http status code 400 series

4xx Client Error
The 4xx class of status code is intended for cases in which the client seems to have erred. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents should display any included entity to the user. These are typically the most common error codes encountered while online.

400 Bad Request
The request cannot be fulfilled due to bad syntax.

401 Unauthorized
Similar to 403 Forbidden, but specifically for use when authentication is possible but has failed or not yet been provided. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource. See Basic access authentication and Digest access authentication.

402 Payment Required
Reserved for future use. The original intention was that this code might be used as part of some form of digital cash or micropayment scheme, but that has not happened, and this code is not usually used. As an example of its use, however, Apple's MobileMe service generates a 402 error ("httpStatusCode:402" in the Mac OS X Console log) if the MobileMe account is delinquent.

403 Forbidden
The request was a legal request, but the server is refusing to respond to it. Unlike a 401 Unauthorized response, authenticating will make no difference.

404 Not Found
The requested resource could not be found but may be available again in the future. Subsequent requests by the client are permissible.

405 Method Not Allowed
A request was made of a resource using a request method not supported by that resource; for example, using GET on a form which requires data to be presented via POST, or using PUT on a read-only resource.

406 Not Acceptable
The requested resource is only capable of generating content not acceptable according to the Accept headers sent in the request.

407 Proxy Authentication Required

408 Request Timeout
The server timed out waiting for the request. According to W3 HTTP specifications: "The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time."

409 Conflict
Indicates that the request could not be processed because of conflict in the request, such as an edit conflict.

410 Gone
Indicates that the resource requested is no longer available and will not be available again. This should be used when a resource has been intentionally removed and the resource should be purged. Upon receiving a 410 status code, the client should not request the resource again in the future. Clients such as search engines should remove the resource from their indices. Most use cases do not require clients and search engines to purge the resource, and a "404 Not Found" may be used instead.

411 Length Required
The request did not specify the length of its content, which is required by the requested resource.

412 Precondition Failed
The server does not meet one of the preconditions that the requester put on the request.

413 Request Entity Too Large
The request is larger than the server is willing or able to process.

414 Request-URI Too Long
The URI provided was too long for the server to process.

415 Unsupported Media Type
The request entity has a media type which the server or resource does not support.For example, the client uploads an image as image/svg+xml, but the server requires that images use a different format.
416 Requested Range Not Satisfiable
The client has asked for a portion of the file, but the server cannot supply that portion. For example, if the client asked for a part of the file that lies beyond the end of the file.

417 Expectation Failed
The server cannot meet the requirements of the Expect request-header field.

418 I'm a teapot
This code was defined in 1998 as one of the traditional IETF April Fools' jokes, in RFC 2324, Hyper Text Coffee Pot Control Protocol, and is not expected to be implemented by actual HTTP servers.

422 Unprocessable Entity (WebDAV) (RFC 4918)
The request was well-formed but was unable to be followed due to semantic errors.

423 Locked (WebDAV) (RFC 4918)
The resource that is being accessed is locked

424 Failed Dependency (WebDAV) (RFC 4918)
The request failed due to failure of a previous request (e.g. a PROPPATCH).

425 Unordered Collection (RFC 3648)
Defined in drafts of "WebDAV Advanced Collections Protocol", but not present in "Web Distributed Authoring and Versioning (WebDAV) Ordered Collections Protocol".

426 Upgrade Required (RFC 2817)
The client should switch to a different protocol such as TLS/1.0.

444 No Response
An Nginx HTTP server extension. The server returns no information to the client and closes the connection (useful as a deterrent for malware).

449 Retry With
A Microsoft extension. The request should be retried after performing the appropriate action.

450 Blocked by Windows Parental Controls
A Microsoft extension. This error is given when Windows Parental Controls are turned on and are blocking access to the given webpage.

499 Client Closed Request
An Nginx HTTP server extension. This code is introduced to log the case when the connection is closed by client while HTTP server is processing its request, making server unable to send the HTTP header back.