Search Results
  1. HTTP (Hypertext Transfer Protocol)
  1. HTTP Status Codes
  1. 501 Not Implemented
    1. Writing responses (servers)
      1. Unknown request method
      2. See also: Method Not Allowed
      3. See also: Expectation failed
    2. Reading responses (clients)
    3. Overview table
    4. Example

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.

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