HTTP 501 Not Implemented

What does HTTP 501 mean?

The server does not support the functionality required to fulfil the request. Usually means the HTTP method is unknown to the server entirely (as opposed to 405, where the server knows the method but the resource does not allow it).

5xx Server error: The request looked valid, but the server failed to fulfil it. The fix is on the server side.

How to fix 501 Not Implemented

• Use a standard method the server supports.

501 and SEO

Pages returning 501 are not indexed.

Example response

HTTP/1.1 501 Not Implemented

How to return a 501 response

Node.js (Express)

res.status(501).json({ error: 'Not Implemented' });

PHP

http_response_code(501);

Python (Flask)

return {'error': 'Not Implemented'}, 501

Go (net/http)

w.WriteHeader(501)

nginx

return 501;

Related status codes

• 405 Method Not Allowed — The URL exists, but does not support the HTTP method used.
• 500 Internal Server Error — The server hit an unexpected condition and could not complete the request.

Check which status code a URL returns with the HTTP header checker.