Client Error · 4xx

451 Unavailable For Legal Reasons

The resource is blocked due to a legal demand.

What 451 Unavailable For Legal Reasons means

451 Unavailable For Legal Reasons (a Ray Bradbury reference, naming intent) signals that content has been blocked due to a legal order: court injunction, DMCA takedown, GDPR right-to-be-forgotten, or government censorship. The response should include details about the legal authority that issued the demand, where possible. 451 is meant to be more transparent than serving 404 or 403 for blocked content.

When servers should return it: Return 451 when content is being withheld specifically due to a legal order, not policy or technical limits.

Example response

HTTP/2 451
link: <https://example.com/legal/notice/dmca-12345>; rel="blocked-by"
content-type: text/html
<p>This content has been removed due to a DMCA takedown notice.</p>

Related status codes

404
Not Found
403
Forbidden
410
Gone

Frequently Asked Questions

Why 451 specifically?
It is named after Fahrenheit 451, Ray Bradbury's novel about book burning and censorship.
Is 451 enforceable?
No. The status code is informational. The legal demand is what is enforceable. 451 just makes the blocking visible.
Defined in: RFC 7725 · Class: 4xx Client Error

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.