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.
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
GET /article/12345 HTTP/1.1 Host: news.example.com HTTP/1.1 451 Unavailable For Legal Reasons Link: <https://regulator.example>; rel="blocked-by" Content-Type: text/html; charset=utf-8