This is a list of Hypertext Transfer Protocol (HTTP) response status codes. HTTP response status codes indicate whether a specific HTTP request has been successfully completed. Responses are grouped in five classes: informational responses, successful responses, redirects, client errors, and servers errors.

Successful responses (2xx)

This class of status codes indicates the action requested by the client was received, understood, accepted, and processed successfully.

200 OK

The request has succeeded. The meaning of a success varies depending on the HTTP method:
GET: The resource has been fetched and is transmitted in the message body.
HEAD: The entity headers are in the message body.
POST: The resource describing the result of the action is transmitted in the message body.
TRACE: The message body contains the request message as received by the server

Redirection messages (3xx)

This class of status code indicates the client must take additional action to complete the request. Many of these status codes are used in URL redirection.

301 Moved Permanently

This response code means that URI of requested resource has been changed. Probably, new URI would be given in the response.

302 Found

This response code means that URI of requested resource has been changed temporarily. New changes in the URI might be made in the future. Therefore, this same URI should be used by the client in future requests.

Client error responses (4xx)

The 4xx class of status code is intended for situations 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

This response means that server could not understand the request due to invalid syntax.

401 Unauthorized

Authentication is needed to get requested response. This is similar to 403, but in this case, authentication is possible.

403 Forbidden

Client does not have access rights to the content so server is rejecting to give proper response.

404 Not Found

Server can not find requested resource. This response code probably is most famous one due to its frequency to occur in web.

Server error responses (5xx)

The server failed to fulfill an apparently valid request.

500 Internal Server Error

The server has encountered a situation it doesn't know how to handle.

502 Bad Gateway

This error response means that the server, while working as a gateway to get a response needed to handle the request, got an invalid response.

503 Service Unavailable

The server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded.

504 Gateway Timeout

This error response is given when the server is acting as a gateway and cannot get a response in time.