HTTP 510 Not Extended

What does HTTP 510 mean?

The request needs further extensions before the server will fulfil it. Defined by the HTTP Extension Framework, which never gained real adoption. You will rarely if ever see it.

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

510 and SEO

Like other 5xx errors: ongoing errors reduce crawling.

Example response

HTTP/1.1 510 Not Extended

How to return a 510 response

Node.js (Express)

res.status(510).json({ error: 'Not Extended' });

PHP

http_response_code(510);

Python (Flask)

return {'error': 'Not Extended'}, 510

Go (net/http)

w.WriteHeader(510)

nginx

return 510;

Related status codes

• 500 Internal Server Error — The server hit an unexpected condition and could not complete the request.
• 501 Not Implemented — The server does not support the functionality required to fulfil the request.
• 505 HTTP Version Not Supported — The server does not support the HTTP version used in the request.

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