The HTTP 451 status code means a client can’t access a resource due to legal reasons.
Some countries routinely send takedown requests to major websites. In such cases, the appropriate status code to return is
451 Unavailable For Legal Reasons.
When the GDPR legislation went into effect, many news websites decided to limit access to their content to European IP addresses by returning the 451 status code.
The server usually includes the
Link HTTP header indicating who ordered the blocking of the resource:
HTTP/2 451 Unavailable For Legal Reasons Link: <https://spqr.example.com/senate>; rel="blocked-by"
Number 451 is a reference to Ray Bradbury’s novel Fahrenheit 451. In the futuristic, dystopian-esque society, books are outlawed and burned by the firemen. 451 °F is a temperature at which book paper combusts.