Client Error 4xx
The 4xx (Client Error) class of status code indicates that the client seems to have erred. Except when responding to a HEAD request, the server SHOULD send a representation 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.
400 Bad Request
The 400 (Bad Request) status code indicates that the server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).
401 Unauthorized
The 401 (Unauthorized) status code indicates that the request has not been applied because it lacks valid authentication credentials for the target resource. The server generating a 401 response MUST send a WWW-Authenticate header field containing at least one challenge applicable to the target resource.
If the request included authentication credentials, then the 401 response indicates that authorization has been refused for those credentials. The user agent MAY repeat the request with a new or replaced Authorization header field.
403 Forbidden
The 403 (Forbidden) status code indicates that the server understood the request but refuses to authorize it.
If authentication credentials were provided in the request, the server considers them insufficient to grant access. The client SHOULD NOT automatically repeat the request with the same credentials. The client MAY repeat the request with new or different credentials. However, a request might be forbidden for reasons unrelated to the credentials.
An origin server that wishes to "hide" the current existence of a forbidden target resource MAY instead respond with a status code of 404 (Not Found).
404 Not Found
The 404 (Not Found) status code indicates that the origin server did not find a current representation for the target resource or is not willing to disclose that one exists. A 404 status code does not indicate whether this lack of representation is temporary or permanent; the 410 (Gone) status code is preferred over 404 if the origin server knows, presumably through some configurable means, that the condition is likely to be permanent.
405 Method Not Allowed
The 405 (Method Not Allowed) status code indicates that the method received in the request-line is known by the origin server but not supported by the target resource. The origin server MUST generate an Allow header field in a 405 response containing a list of the target resource's currently supported methods.
406 Not Acceptable
The 406 (Not Acceptable) status code indicates that the target resource does not have a current representation that would be acceptable to the user agent, according to the proactive negotiation header fields received in the request , and the server is unwilling to supply a default representation.
The server SHOULD generate a payload containing a list of available representation characteristics and corresponding resource identifiers from which the user or user agent can choose the one most appropriate.
415 Unsupported Media Type
The 415 (Unsupported Media Type) status code indicates that the origin server is refusing to service the request because the payload is in a format not supported by this method on the target resource. The format problem might be due to the request's indicated Content-Type or Content-Encoding, or as a result of inspecting the data directly.
Server Error 5xx
The 5xx (Server Error) class of status code indicates that the server is aware that it has erred or is incapable of performing the requested method. Except when responding to a HEAD request, the server SHOULD send a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition. A user agent SHOULD display any included representation to the user. These response codes are applicable to any request method.
500 Internal Server Error
The 500 (Internal Server Error) status code indicates that the server encountered an unexpected condition that prevented it from fulfilling the request.