The first line of the response message (i.e., the status line) contains the response status code, which is generated by the server to indicate the outcome of the request.
The status code is a 3-digit number:
1xx (Informational): Request received, server is continuing the process.2xx (Success): The request was successfully received, understood, accepted and serviced.3xx (Redirection): Further action must be taken in order to complete the request.4xx (Client Error): The request contains bad syntax or cannot be understood.5xx (Server Error): The server failed to fulfill an apparently valid request.Some commonly encountered status codes are:
100 Continue: The server received the request and in the process of giving the response.200 OK: The request is fulfilled.301 Move Permanently: The resource requested for has been permanently moved to a new location. The URL of the new location is given in the response header called Location. The client should issue a new request to the new location. Application should update all references to this new location.302 Found & Redirect (or Move Temporarily): Same as 301, but the new location is temporarily in nature. The client should issue a new request, but applications need not update the references.304 Not Modified: In response to the If-Modified-Since conditional GET request, the server notifies that the resource requested has not been modified.400 Bad Request: Server could not interpret or understand the request, probably syntax error in the request message.401 Authentication Required: The requested resource is protected, and require client’s credential (username/password). The client should re-submit the request with his credential (username/password).403 Forbidden: Server refuses to supply the resource, regardless of identity of client.404 Not Found: The requested resource cannot be found in the server.405 Method Not Allowed: The request method used, e.g., POST, PUT, DELETE, is a valid method. However, the server does not allow that method for the resource requested.408 Request Timeout:414 Request URI too Large:500 Internal Server Error: Server is confused, often caused by an error in the server-side program responding to the request.501 Method Not Implemented: The request method used is invalid (could be caused by a typing error, e.g., "GET" misspell as "Get").502 Bad Gateway: Proxy or Gateway indicates that it receives a bad response from the upstream server.503 Service Unavailable: Server cannot response due to overloading or maintenance. The client can try again later.504 Gateway Timeout: Proxy or Gateway indicates that it receives a timeout from an upstream server.