HTTP Status Code 501 – Not Implemented
The HTTP status code 501 Not Implemented indicates that the server does not support the functionality required to fulfill the request. This status code essentially states that the server recognizes the request method, but it is not supported by the server for the requested resource.
Examples
Example 1: Unsupported HTTP Method
Consider a server that only supports GET and POST methods. If a client sends a request using the PATCH method, which is not supported, the server would respond with a 501 status code.
Request: PATCH /api/users/123 HTTP/1.1
Host: example.com
Response: HTTP/1.1 501 Not Implemented
Date: Wed, 13 Oct 2023 15:00:00 GMT
Server: Apache/2.4.41 (Ubuntu)
Content-Type: text/html; charset=UTF-8
Content-Length: 230
<html><head><title>501 Not Implemented</title></head><body><h1>Not Implemented</h1><p>The server does not support the functionality required to fulfill the request.</p></body></html>
Example 2: Unimplemented Feature
Suppose a RESTful API is under development, and a client sends a request to an endpoint for a feature that hasn’t been implemented yet.
Request: DELETE /api/orders/456 HTTP/1.1
Host: example.com
Response: HTTP/1.1 501 Not Implemented
Date: Wed, 13 Oct 2023 16:00:00 GMT
Server: Nginx/1.18.0 (Ubuntu)
Content-Type: text/html; charset=UTF-8
Content-Length: 215
<html><head><title>501 Not Implemented</title></head><body><h1>Not Implemented</h1><p>The requested feature is not yet supported by the server.</p></body></html>
Example 3 Scenario
# Client sends a request example.
GET /example HTTP/1.1
Host: www.example.com
# Server Response
HTTP/1.1 501 501 Not Implemented
Date: Wed, 09 Oct 2024 23:10:14 GMT
Server: ExampleServer/1.0
Content-Type: application/json
{
"error": "Description of the error for 501"
}
Example 4 Scenario
# Client sends another example request.
POST /another-example HTTP/1.1
Host: www.example.com
# Server Response
HTTP/1.1 501 501 Not Implemented
Date: Wed, 09 Oct 2024 23:10:14 GMT
Server: ExampleServer/1.0
Content-Type: application/json
{
"error": "Detailed message for 501"
}
Summary
The 501 Not Implemented status code signifies that the server either does not recognize or cannot fulfill the request method due to lack of support for the requested functionality. It is commonly used when features or methods are not yet available on the server. Understanding and handling this status code can help guide further steps, such as updating server capabilities or informing users about unsupported features.
