HTTP Status Codes
The HTTP server responses are classified by a numerical status code. Status codes indicate the reasons behind successful and failed HTTP requests. The IANA maintains the official registry of the HTTP status codes.
Status codes starting with 1xx are Informational, 2xx are Success, 3xx are Redirection, 4xx are Client Error, and 5xx are Server Error.
Common status codes include the following:
100 = Continue: The server has received the request headers and the client should proceed to send the request body (in the case of a request for which a body needs to be sent; for example, a POST request).
200 = OK: The processing of the request that was sent by the client was successful.
301 = Moved Permanently: The resource has permanently moved to a different URI.
302 = Found: The requested resource resides temporarily under a different URI. The client is invited by a response with this code to make a second, otherwise identical, request to the new URL specified in the location field. However, many web browsers implemented the 302 status code in a manner that violates the HTTP/1.0 specification, changing the request type of the new request. Therefore, one of the other status codes that was added with the HTTP/1.1 specification is status code 307.
307 = Temporarily Moved: The request should be repeated with another URI; however, future requests should still use the original URI. The 307 status code indicates to client that the request method should not be changed when reissuing the original request. For example, a POST request should be repeated using another POST request.
401 = Unauthorized (Authentication Required): The request first requires authentication with the server.
403 = Forbidden: Access is denied.
404 = Not Found: The server cannot find the requested URI.
407 = Proxy Authentication Required: The request first requires authentication with the proxy.
500 = Internal Server Error: This generic web server error message is given when an unexpected condition is encountered and no more specific message is suitable.