What are Response Codes / HTTP Status codes?
When a search engine or website visitor makes a request to a web server, a three-digit HTTP Response Status Code is returned. This code indicates what is about to happen. HTTP response status codes indicate whether a specific HTTP request has been successfully completed.
These responses are divided into 5(five) categories listed below:
Informational responses (100–199)
Successful responses (200–299)
Redirects (300–399)
Client errors (400–499)
Server errors (500–599)
Informational responses
- 100 Continue
This interim response indicates that everything so far is OK and that the client should continue the request, or ignore the response if the request is already finished.
- 101 Switching Protocol
This code is sent in response to an Upgrade request header from the client and indicates the protocol the server is switching to.
Successful responses
- 200 OK
The request has succeeded. The meaning of success depends on the HTTP method: (GET, PUT, POST)
- 201 Created
The request has succeeded and a new resource has been created as a result. This is typically the response sent after POST requests or some PUT requests.
- 202 Accepted
The request has been received but not yet acted upon. It is noncommittal since there is no way in HTTP to later send an asynchronous response indicating the outcome of the request. It is intended for cases where another process or server handles the request, or for batch processing.
- 203 Non-Authoritative Information
This response code means the returned meta-information is not exactly the same as is available from the origin server but is collected from a local or a third-party copy. This is mostly used for mirrors or backups of another resource. Except for that specific case, the "200 OK" response is preferred to this status.
- 204 No Content
There is no content to send for this request, but the headers may be useful. The user-agent may update its cached headers for this resource with the new ones.
- 205 Reset Content
Tells the user-agent to reset the document which sent this request.
Redirection messages
- 300 Multiple Choice
The request has more than one possible response. The user-agent or user should choose one of them. (There is no standardized way of choosing one of the responses, but HTML links to the possibilities are recommended so the user can pick.)
- 301 Moved Permanently
The URL of the requested resource has been changed permanently. The new URL is given in the response.
Client error responses
- 400 Bad Request
The server could not understand the request due to invalid syntax.
- 401 Unauthorized
Although the HTTP standard specifies "unauthorized", semantically this response means "unauthenticated". That is, the client must authenticate itself to get the requested response.
- 402 Payment Required
This response code is reserved for future use. The initial aim for creating this code was using it for digital payment systems, however, this status code is used very rarely and no standard convention exists.
- 403 Forbidden
The client does not have access rights to the content; that is, it is unauthorized, so the server is refusing to give the requested resource. Unlike 401, the client's identity is known to the server.
- 404 Not Found
The server can not find the requested resource. In the browser, this means the URL is not recognized. In an API, this can also mean that the endpoint is valid but the resource itself does not exist. Servers may also send this response instead of 403 to hide the existence of a resource from an unauthorized client. This response code is probably the most famous one due to its frequent occurrence on the web.
- 405 Method Not Allowed
The request method is known by the server but has been disabled and cannot be used. For example, an API may forbid DELETE-ing a resource. The two mandatory methods, GET and HEAD, must never be disabled and should not return this error code.
- 406 Not Acceptable
This response is sent when the webserver, after performing server-driven content negotiation, doesn't find any content that conforms to the criteria given by the user agent.
- 407 Proxy Authentication Required
This is similar to 401 but authentication is needed to be done by a proxy.
- 411 Length Required
The server rejected the request because the Content-Length header field is not defined and the server requires it.
- 412 Precondition Failed
The client has indicated preconditions in its headers which the server does not meet.
- 413 Payload Too Large
Request entity is larger than limits defined by the server; the server might close the connection or return a Retry-After header field.
- 414 URI Too Long
The URI requested by the client is longer than the server is willing to interpret.
Server error responses
- 500 Internal Server Error
The server has encountered a situation it doesn't know how to handle.
- 501 Not Implemented
The request method is not supported by the server and cannot be handled. The only methods that servers are required to support (and therefore that must not return this code) are GET and HEAD.
- 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. Note that together with this response, a user-friendly page explaining the problem should be sent.
- 504 Gateway Timeout
This error response is given when the server is acting as a gateway and cannot get a response in time.
- 505 HTTP Version Not Supported
The HTTP version used in the request is not supported by the server.
- 506 Variant Also Negotiates
The server has an internal configuration error: the chosen variant resource is configured to engage in transparent content negotiation itself and is therefore not a proper endpoint in the negotiation process.
For more response codes description visit Mozilla Developer Network