(HTTP) Hypertext Transfer Protocol. The status code is part of the HTTP, The Internet Assigned Numbers Authority (IANA) maintains the official registry of HTTP status codes. Microsoft Internet Information Services (IIS) sometimes uses additional decimal sub-codes for more specific information.
Informational 1xx: The initial part of a request has been received and the process is not rejected by the server. The server intends to send a final response after the request has been fully received and acted upon. When the request contains an Expect header field that includes a 100-continue -expectation.
Success 2xx: HTTP 200 means transmission is OK on the HTTP level. This has nothing to do with success or failure of your code. In this case,the HTTP 200 indicates that your code error message was successfully transferred
GET an entity corresponding to the requested resource is sent in the response;
HEAD the entity-header fields corresponding to the requested resource are sent in the response without any message-body;
POST an entity describing or containing the result of the action;
TRACE an entity containing the request message as received by the end server.
202 Accepted: The request has been accepted for processing, but the processing has not been completed. The request might or might not eventually be acted upon, as it might be disallowed when processing actually takes place. There is no facility for re-sending a status code from an asynchronous operation such as this.
203 Non-Authoritative Information: The request was successful but the enclosed payload has been modified from that of the origin server's 200 OK response by a transforming proxy.
204 No Content: The server successfully processed the request, but is not returning any content. Unlike a 204 response.
205 Reset Content: The server successfully processed the request, but is not returning any content. Unlike a 204 response.
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. A user agent may carry out the additional action with no user interaction only if the method used in the second request is GET or HEAD. A user agent may automatically redirect a request. A user agent should detect and intervene to prevent cyclical redirects.
302 Found: The target resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client ought to continue to use the effective request URI for future requests.
304 Not Modified: If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server SHOULD respond with this status code. The 304 response MUST NOT contain a message-body and thus is always terminated by the first empty line after the header fields.
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: The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.
401 Unauthorized: The request has not been applied because it lacks valid authentication credentials for the target resource.
402 Payment Required: This code is reserved for future use.
404 Not Found: The requested resource could not be found but may be available in the future. Subsequent requests by the client are permissible.
405 Method Not Allowed: The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response MUST include an Allow header containing a list of valid methods for the requested resource.
408 Request Timeout: 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.
411 Length Required: The server refuses to accept the request without a defined Content-Length.
414 Request-URI Too Long : It provided too long for the server to process. Often the result of too much data being encoded as a query-string of a GET request, in which case it should be converted to a POST request. Called "Request-URI Too Long" previously.
415 Unsupported Media Type: The requesting entity has a media type which the server or resource does not support. For example, the client uploads an image as but the server requires that images use a different format.
417 Expectation Failed: The server cannot meet the requirements of the Expect request-header field.
Server errors 5xx: The server encountered an unexpected condition that 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, while acting as a gateway or proxy, received an invalid response from an inbound server it accessed while attempting to fulfill the request.
505 HTTP Version Not Supported: The server does not support the HTTP protocol version used in the request.