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451 Unavailable For Legal Reasons

Access is denied because of a legal demand, such as a court order or a statutory blocking requirement.

Status

HTTP/1.1 451 Unavailable For Legal Reasons

Details

  • Category: 4xx
  • Status: Standard. Registered with IANA and defined by a current standards-track RFC.
  • Specification: RFC 7725
  • Cacheable: Cacheable by default
  • Response body: Allowed
  • Retry: Do not retry

451 exists so that legal blocking is visible rather than disguised as a technical failure. The number is a reference to Fahrenheit 451. The specification asks the server to explain the block in the body and to identify the entity making the demand where possible.

A Link header with rel="blocked-by" identifies the blocking authority. Note that this describes the party demanding the block, not necessarily the operator of the server returning it.

Note: The Link header with rel="blocked-by" identifies the party demanding the block, which is not necessarily the operator of the server returning the response.

Headers

  • Link: With rel="blocked-by", identifying the entity that demanded the block.

Common causes

  • A court order or regulator requiring removal in a jurisdiction.
  • Geographic restrictions imposed by licensing or sanctions rules.
  • Statutory takedown obligations applied to specific content.

How to fix it

As the client

  • Recognize that the restriction is jurisdictional rather than technical, and read the body for scope.
  • Do not retry. The block will not clear through repetition.

As the server

  • Explain what is blocked, for whom, and by whose demand, to the extent the law allows.
  • Use 451 rather than 403 or 404 when the cause is legal, so the block is transparent.

Examples

Content blocked by a legal demand

HTTP request

GET /article/12345 HTTP/1.1
Host: news.example.com

HTTP response

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

Specifications

See also