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451 Unavailable For Legal Reasons: blocked by a legal demand

451 Unavailable For Legal Reasons means access to a resource is denied because of a legal demand, such as a court order or national block.

Check a URL’s status code

451 Unavailable For Legal Reasons tells the client that access to a resource is denied because of a legal demand: a court order, a government block, a regulation in the visitor’s country. The number is a nod to Ray Bradbury’s Fahrenheit 451.

Definition

RFC 7725 (2016) defines 451 for a server that is “denying access to the resource as a consequence of a legal demand.” The server sending it isn’t necessarily the origin; an ISP or a national filter can send it too. The RFC asks that responses:

  • explain the legal demand in the body, including who made it and which law applies, where that’s possible;
  • include a Link header with rel="blocked-by" identifying the party implementing the block, not the one demanding it.

A 451 is cacheable by default, like a 404 or 410.

When it’s used

  • Content removed or geo-blocked after a court order or takedown notice.
  • Pages withheld in specific countries for regulatory reasons; several US news sites famously blocked EU visitors with 451 when GDPR took effect in 2018.
  • Network-level blocking by ISPs that choose to be transparent about it.

SEO impact

Google treats 451 like any 4xx except 429: the URL isn’t indexed and existing entries are removed (Google’s documentation). Be careful with geo-blocking. Googlebot crawls mainly from IP addresses in the United States, so if you return 451 to US visitors, Google sees the block and can drop those pages from results everywhere. If you must block a country, block it consistently and accept the effect on search, rather than making a special exception for Googlebot.

How to implement and check

HTTP/1.1 451 Unavailable For Legal Reasons
Link: <https://hosting.example.net/legal-requests>; rel="blocked-by"
Content-Type: text/html; charset=utf-8

<p>This page is unavailable in your country following a court order
(case 2026/1234, Example District Court).</p>

Use 451 instead of a vague 403 when the reason is legal: it’s honest with visitors and machine-readable for researchers who track censorship. The HTTP header checker shows the status and Link header as seen from our servers, and the HTTP status checker confirms which URLs are affected.

Frequently asked questions

What is the difference between 451 and 403?

403 is a general refusal. 451 says specifically that the refusal is due to a legal demand, and the response should explain which one and who is blocking access.

Will a 451 remove my page from Google?

If Googlebot receives the 451, yes: Google treats it like other 4xx codes and drops the URL. Since Googlebot mostly crawls from the United States, a block on US visitors usually means the page disappears from Google.

Why is the code 451?

It refers to Fahrenheit 451, Ray Bradbury’s novel about book burning and censorship. The number was chosen deliberately when RFC 7725 defined the code in 2016.