HTTP 505 HTTP Version Not Supported
Updated Free mock REST & WebSocket APIs
HTTP 505 HTTP Version Not Supported — The server doesn't support the HTTP protocol version used in the request.
- Class
- 5xx Server Error
- Defined in
- RFC 9110 §15.6.6
- Official
- Yes (IANA registry)
- Cacheable by default
- No (unless Cache-Control/Expires say so)
- Safe to retry
- Sometimes — idempotent requests only
Try it: get a real 505 response
Our test endpoint answers every request with 505 HTTP Version Not Supported.
curl -i https://mockfox.dev/api/status/505Use it in tests, health-check monitors or to see how your client handles a 505. Add ?delay=2000 to slow it down.
What does HTTP 505 mean?
Very rare: it appears when a client sends a malformed request line (for example spaces in an unencoded URL make the server misread the version) or an HTTP version the server refuses, such as HTTP/0.9 or a garbled HTTP/1.2. Encode spaces as %20 in URLs and let your HTTP library build the request line.
How to fix 505
- Visitors: This is a server-side problem — wait a moment and retry, or check the site's status page.
- Developers: Check application and proxy logs at the time of the error, verify upstream services are healthy, and alert on 5xx rates.
Example 505 response
HTTP/1.1 505 HTTP Version Not Supported
Content-Type: application/json
{"status":505,"error":"HTTP Version Not Supported"}5xx Server Error: The server failed to fulfill a valid request — usually temporary, or a server-side bug. See the full list of HTTP status codes.
Related status codes
- 400 Bad RequestThe server can't process the request because it's malformed or invalid.
- 426 Upgrade RequiredThe server refuses to handle the request over the current protocol; the Upgrade header names the required one.
- 501 Not ImplementedThe server doesn't support the functionality (usually the HTTP method) needed to fulfill the request.
Related tools
Frequently asked questions
What does HTTP 505 HTTP Version Not Supported mean?
The server doesn't support the HTTP protocol version used in the request.
Is 505 a client or a server error?
505 is a 5xx code: the server failed to handle a request that may be perfectly valid. It's often temporary.
Where is 505 defined?
In RFC 9110 §15.6.6. It's listed in the IANA HTTP Status Code Registry.
How can I test how my app handles a 505?
Call https://mockfox.dev/api/status/505 — it responds with 505 to any method, with CORS enabled. Add ?delay=2000 to simulate a slow response.