HTTP 505 HTTP Version Not Supported

What does HTTP 505 mean?

The server does not support the HTTP version used in the request. Rare today; it can appear with very old servers or when a client sends a malformed request line.

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

505 and SEO

Rare; pages returning 505 are not indexed.

Example response

HTTP/1.1 505 HTTP Version Not Supported

How to return a 505 response

Node.js (Express)

res.status(505).json({ error: 'HTTP Version Not Supported' });

PHP

http_response_code(505);

Python (Flask)

return {'error': 'HTTP Version Not Supported'}, 505

Go (net/http)

w.WriteHeader(505)

nginx

return 505;

Related status codes

• 400 Bad Request — The server cannot process the request because it is malformed.
• 426 Upgrade Required — The server requires the client to switch to a different protocol.

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