Abbrev. from RFC2616 Section 10....

10.1 Informational 1xx

This class of status code indicates a provisional response, consisting only of the Status-Line and optional headers, and is terminated by an empty line. There are no required headers for this class of status code. Since HTTP/1.0 did not define any 1xx status codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client except under experimental conditions.

 100 Continue
 101 Switching Protocols

10.2 Successful 2xx

This class of status code indicates that the client’s request was successfully received, understood, and accepted.

 200 OK
 201 Created
 202 Accepted
 203 Non-Authoritative Information
 204 No Content
 205 Reset Content
 206 Partial Content

10.3 Redirection 3xx

This class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request. The action required MAY be carried out by the user agent without interaction with the user if and only if the method used in the second request is GET or HEAD. A client SHOULD detect infinite redirection loops, since such loops generate network traffic for each redirection.

 300 Multiple Choices
 301 Moved Permanently
 302 Found
 303 See Other
 304 Not Modified
 305 Use Proxy
 306 (Unused)
 307 Temporary Redirect

10.4 Client Error 4xx

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.

 400 Bad Request
 401 Unauthorized
 402 Payment Required
 403 Forbidden
 404 Not Found
 405 Method Not Allowed
 406 Not Acceptable
 407 Proxy Authorization Required
 408 Request Timeout
 409 Conflict
 410 Gone
 411 Length Required
 412 Precondition Failed
 413 Request Entity Too Large
 414 Request-URI Too Long
 415 Unsupported Media Type
 416 Requested Range Not Satisfiable
 417 Expectation Failed  (''nb: most humans register this on a regular   basis'')

10.5 Server Error 5xx

Response status codes beginning with the digit “5” indicate cases in which the server is aware that it has erred or is incapable of performing the request. 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. User agents SHOULD display any included entity to the user. These response codes are applicable to any request method.

 500 Internal Server Error
 501 Not Implemented
 502 Bad Gateway
 503 Service Unavailable
 504 Gateway Timeout
 505 HTTP Version Not Supported