HTTP 451 Unavailable For Legal Reasons

Client error code, RFC 7725

What it means

The page is blocked for legal reasons, for example a court order or a law, and the response says so.

A real response

This is the request and the answer our test server gave when we asked it to return 451.

GET /c/451 HTTP/1.1
Host: example.com

HTTP/1.1 451 Unavailable For Legal Reasons
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

RFC 7725 defines 451 and suggests (does not require) a Link header with rel="blocked-by" that names who blocked it. Explain in the body what was blocked and, if allowed, why.

If you are a visitor

The block is deliberate. The site cannot help; asking for the legal basis is a matter for the blocking party.

A common mistake

Using 403 or 404 for a legal block, which hides the reason.

Registered in the IANA HTTP Status Code Registry as Unavailable For Legal Reasons, defined in RFC 7725.

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.