HTTP Status Codes

505 HTTP Version Not Supported

The server does not support, or refuses to support, the HTTP protocol version used in the request.

What it means

505 HTTP Version Not Supported means the major HTTP version in the request line is one the server will not handle. It is rare in practice, since clients and servers negotiate versions, but can appear with malformed requests or deliberately restricted servers.

Why it matters

  • It reports a protocol-level incompatibility distinct from application errors.

Common mistakes

  • Confusing a 505 with a TLS/ALPN negotiation failure, which happens below HTTP.

How WebInspect checks this

  • WebInspect reports negotiated HTTP versions (1.1/2/3) and ALPN details.