HTTP 501 Not Implemented — What It Means and How to Fix It

The HTTP 501 (Not Implemented) status code indicates that the server does not support the functionality required to fulfill the request. This usually means the server does not recognize the request method or lacks the ability to complete the request for some other reason.

Last updated: 2026-06-11

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                Status Code
                501
            

Name Not Implemented

Common Causes

The server does not recognize or support the HTTP method used in the request (e.g., a custom or non-standard method).
The server is a proxy and does not support the requested protocol version or a specific feature required by the client.
The server is intentionally configured to not implement certain functionalities or methods.

Code Examples to Handle HTTP 501

curl -I https://httpbin.org/status/501

fetch('https://httpbin.org/status/501')
  .then(response => {
    if (response.status === 501) {
      console.log('Handled Not Implemented');
    }
  });

import requests

response = requests.get('https://httpbin.org/status/501')
if response.status_code == 501:
    print("Received Not Implemented")

How to Fix It

Verify the HTTP method being used in the request. Ensure it is a standard method (GET, POST, PUT, DELETE, etc.) and that the server is expected to support it.
If acting as a client, check the server's documentation or API specifications to understand which methods and functionalities it supports.
If you are the server administrator, review the server's configuration and code to ensure that the requested functionality or method is properly implemented and enabled.

💡 Example: A client attempts to use a custom HTTP method, `PATCH_ALL`, on a REST API endpoint. The server, which only supports standard `GET`, `POST`, `PUT`, and `DELETE` methods, responds with a 501 Not Implemented status code because it doesn't recognize or have the logic for `PATCH_ALL`.

🛠️ Developer Tip: When developing APIs, ensure that your server explicitly handles all supported HTTP methods and returns a 501 for any unsupported ones, rather than an unexpected error. This provides clear feedback to clients.

Related Status Codes

Frequently Asked Questions

What causes HTTP 501?

HTTP 501 is caused when the server does not possess the capability to fulfill the request, typically because it doesn't recognize or support the HTTP method used, or a specific feature required by the request.

How do I fix HTTP 501?

To fix HTTP 501, clients should verify they are using standard and supported HTTP methods. Server administrators need to ensure their server is configured to handle the requested functionality or method, or update their server's capabilities if the functionality is desired.