HTTP 406 Not Acceptable

Client error code, RFC 9110, section 15.5.7

What it means

The server cannot produce an answer in a format that the request said it would accept (its Accept headers).

A real response

This is the request and the answer our test server gave when we asked it to return 406.

GET /c/406 HTTP/1.1
Host: example.com

HTTP/1.1 406 Not Acceptable
Date: Sat, 14 Nov 2026 10:00:00 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 11

<p>demo</p>

If you run the site

This is content negotiation failing. A client asked, for example, for XML only, and the server has only JSON. Either support more formats or ignore the Accept header and send what you have, which many sites choose to do. A browser rarely causes 406; security modules that reject unusual requests sometimes do.

If you are a visitor

Try a different browser or turn off extensions that change request headers.

A common mistake

Strict Accept handling that rejects requests from tools that send Accept: */* only partly.

Registered in the IANA HTTP Status Code Registry as Not Acceptable, defined in RFC 9110, section 15.5.7.

This is an independent guide. It is not connected with the IETF, IANA, any browser maker or any company named here. Meanings were checked against the RFC texts on 14 November 2026. Responses shown were recorded on 14 November 2026 from a small test server on the author's own computer.