HTTP 505 — HTTP Version Not Supported
5xx Server Error
What it means
The server does not support the HTTP protocol version the client used.
What to do about it
Rare. Usually a misconfigured client or an old proxy speaking HTTP/0.9.
Where it sits
505 belongs to the 5xx family: The server failed to fulfil an apparently valid request. The fix is on the server side.
HTTP/1.1 505 HTTP Version Not SupportedChecking it yourself
# see the status code and headers only
curl -sI https://example.com/path
# follow redirects and print each hop
curl -sIL -o /dev/null -w "%{http_code} %{url_effective}\n" https://example.com/path
# JavaScript
const r = await fetch(url);
console.log(r.status, r.statusText);How this code behaves
| Cacheable by default | No — caches must not store this response unless explicit cache headers permit it. |
| Safe to retry | Yes, with backoff. This is a transient condition; retrying the same request is reasonable. |
| Effect on search indexing | Repeated server errors reduce crawl rate and eventually drop pages from the index. |
Returning 505 correctly
# nginx
return 505;
# Express
res.status(505).json({ error: 'HTTP Version Not Supported' });
# Go
w.WriteHeader(505)
# Python (Flask)
return jsonify(error='HTTP Version Not Supported'), 505;Frequently asked questions
What does HTTP 505 mean?
The server does not support the HTTP protocol version the client used.
How do I fix a 505 error?
Rare. Usually a misconfigured client or an old proxy speaking HTTP/0.9.
Is 505 a client or server problem?
A server problem. The request was valid; the server failed to fulfil it. Nothing the client changes will help.