HTTP 505 — HTTP Version Not Supported

Server error responses (5xx) · Updated 2026-10-18

HTTP 505 rejects the protocol version in the request line: the server refuses to speak that version for this resource, whether it is too old or, occasionally, too new for its stack.

When 505 shows up

Clients pinning an old HTTP version against a modernised server.
Protocol enforcement policies at gateways.

Mocking a 505 response

A response with this status can be faked end to end with a local mock rule — no backend changes needed. The configuration below mirrors the rule fields the ApiSimul editor uses (method, path, status, delay in milliseconds, response body):

{
  "method": "GET",
  "path": "/api/data",
  "status": 505,
  "delay": 170,
  "enabled": true,
  "body": null
}

Dynamic placeholders such as {{random.name}}, {{string.uuid}} or {{number.int 1 100}} can appear inside the body to vary each response, which keeps client-side list rendering and retry logic honest during development.

Frequently asked questions

What does HTTP 505 mean?
The HTTP version in the request is not supported. The client must negotiate a version the server does speak.

How can I test a 505 response without a real backend?
Define a mock rule with the method and path your client requests and set the status to 505. The example configuration above returns this response after the listed delay, so the client exercises its 505 handling exactly as it would against a live server.

Related status codes

500 Internal Server Error 501 Not Implemented 502 Bad Gateway 503 Service Unavailable 504 Gateway Timeout 506 Variant Also Negotiates 507 Insufficient Storage 508 Loop Detected 510 Not Extended 511 Network Authentication Required

Need the response in your own project? Spin up rules for any status with the ApiSimul mock server, or browse every status code page.