501 Not Implemented
The 501 (Not Implemented) HTTP status code indicates indicates the server does not support the functionality required to fulfill the request.
Writing responses (servers)
Unknown request method
The primary purpose is to indicate the server is unfamiliar with the requested method. This status code is emitted after the request headers have been parsed, before the resource is looked up. The response should include a document listing the supported methods, or link to documentation describing the supported methods.
See also: Method Not Allowed
Unlike 405 Method Not Allowed
, the server does not need to send an Allow
header, since the server has not yet looked up the resource to know what those methods might be.
If the server supports the requested method, and has looked up the resource, but the resource does not support the request method, see 405 Method Not Allowed.
See also: Expectation failed
The Expect header can be used to indicate a client requires a specific feature from a server. Failure to meet this requirement will generate a separate status code, 417 Expectation Failed.
Reading responses (clients)
The client can reissue the request modified to use a different method, if there is a way to do so.
Overview table
- Name
- 501
- Message
- 501 Not Implemented
- Description
- The server does not support the functionality required to fill the request.
- Specification
- RFC 7231: HTTP/1.1 Semantics and Content ยง6.6.2. 501 Not Implemented
Example
HTTP/1.0 501 Not Implemented
Content-Type: text/plain
The "MGET" method is not recognised by this server.
See <http://example.com/help> for information on our offerings.