What 505 HTTP Version Not Supported means

505 HTTP Version Not Supported is rare. Modern servers handle HTTP/1.0, HTTP/1.1, HTTP/2, and HTTP/3 ubiquitously. 505 mostly shows up for very old HTTP/0.9 clients hitting modern servers, or for handcrafted requests with malformed version strings.

When servers should return it: Return 505 when a request specifies an HTTP major version the server does not implement.

How to fix 505 HTTP Version Not Supported

  • Use a modern HTTP client
  • Verify the request line has a valid HTTP version (HTTP/1.1, HTTP/2.0)

Example response

HTTP/1.1 505
content-type: text/plain
HTTP version not supported

More references

For a one-page reference of all HTTP status codes, see the HTTP cheat sheet. For testing API responses, try the API Tester tool. For inspecting responses on the command line, the curl cheat sheet covers the most common flags.