Takeaways
- The server is denying access to the resource as a consequence of a legal demand.
- The server in question might not be an origin server. This type of legal demand typically most directly affects the operations of ISPs and search engines.
- Responses using this status code should include an explanation, in the response body, of the details of the legal demand: the party making it, the applicable legislation or regulation, and what classes of person and resource it applies to.
Example
HTTP/1.1 451 Unavailable For Legal Reasons
Link: <https://spqr.example.org/legislatione>; rel="blocked-by"
Content-Type: text/html<html>
<head>
<title>Unavailable For Legal Reasons</title>
</head>
<body>
<h1>Unavailable For Legal Reasons</h1>
<p>This request may not be serviced in the Roman Province
of Judea due to the Lex Julia Majestatis, which disallows
access to resources hosted on servers deemed to be
operated by the People's Front of Judea.</p>
</body>
</html>NoteThe
Linkheader might also contain arel="blocked-by"relation identifying the entity and implementing blockage, not any other entity mandating it.
The use of the 451 status code implies neither the existence nor non- existence of the resource named in the request. That is to say, it is possible that if the legal demands were removed, a request for the resource still might not succeed.
Note that in many cases clients can still access the denied resource by using technical countermeasures such as a VPN or the Tor network.
A 451 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls.
Information
This status code got it's number from the book Fahrenheit 451 by Ray Bradbury.