HTTP 510 Not Extended
Further extensions to the request are required for the server to fulfill it.
5xx Server Error
510
Not Extended
Description
The 510 Not Extended status code indicates that further extensions to the request are required for the server to fulfill it. The server should include information about the required extensions in the response. This is an experimental status code defined in RFC 2774 (An HTTP Extension Framework) and is very rarely seen in practice. It was designed for a proposed extension mechanism where clients and servers negotiate protocol extensions.
When Is It Used?
Designed for the HTTP Extension Framework where additional protocol extensions are needed to fulfill a request. This is an experimental status code that is extremely rare in practice and is unlikely to be encountered in normal web development.
Example Response
HTTP/1.1 510 Not Extended
Content-Type: text/plain
An extension is required to fulfill this request.