Accept Nonsense — HTTP/1.1 Compliance

What it sends

A GET request with an Accept header requesting a non-existent media type.

GET / HTTP/1.1\r\n
Host: localhost:8080\r\n
Accept: application/x-nonsense\r\n
\r\n

What the RFC says

"A request without any Accept header field implies that the user agent will accept any media type in response." — RFC 9110 §12.5.1

"If the header field is present in a request and none of the available representations for the response have a media type that is listed as acceptable, the origin server can either honor the header field by sending a 406 (Not Acceptable) response or disregard the header field by treating the response as if it is not subject to content negotiation for that request." — RFC 9110 §12.5.1

Why it matters

Content negotiation allows servers to serve different representations of a resource based on client capabilities. A server that returns 406 Not Acceptable for unrecognized media types actively enforces content negotiation. A server that ignores the Accept header and serves a default representation is also compliant — the RFC explicitly allows both behaviors.

Verdicts

• Pass — Server returns 406 Not Acceptable (enforces content negotiation)
• Warn — Server returns 2xx (ignores Accept, serves default representation)
• Fail — Server returns an unexpected error status

Sources

• RFC 9110 §12.5.1