The Internet Engineering Task Force (IETF), the body responsible for overseeing the internet's technical standards, has approved HTTP 451, "an HTTP Status Code to Report Legal Obstacles". The new status code will show viewers when a web page is being blocked for legal reasons.

Although the IETF's steering group initially resisted the 2013 proposal for error 451, made by then-Google engineer Tim Bray, a rise in online censorship led to the draft proposal getting the support it needed.


IETF chair Mark Nottingham writes that "as censorship became more visible and prevalent on the Web, we started to hear from sites that they'd like to be able to make this distinction. More importantly, we started to hear from members of the community that they wanted to be able to discover instances of censorship in an automated fashion."

It was ultimately this need for machine-readable statistics on censorship that carried the proposal through to full approval as part of the Internet Standards. Although the approval is likely to see the fairly rapid implementation of HTTP 451 Unavailable For Legal Reasons in server software such as Apache, its use online will spread more slowly, as and when server owners patch up to the latest versions.


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Just because the standard exists doesn't necessarily mean that it'll be used. Reasonably well-informed speculation inserted into the current Wikipedia entry for HTTP 451 observes that "some sites may be forced to produce HTTP 404 (File Not Found) or similar, if they are not legally permitted to disclose that the resource has been removed", citing that some UK ISPs' implementation of the Internet Watch Foundation blacklist as example of instances where an HTTP 404 error is returned by design. BT's Cleanfeed is referenced as a key example.

"I suspect that censorious governments will disallow the use of 451, to hide what they're doing," Nottingham wrote, on a similar note. "We can't stop that (of course), but if your government does that, it sends a strong message to you as a citizen about what their intent is. That's worth knowing about, I think."

The new error's number, 451, is a reference to Ray Bradbury's novel Fahrenheit 451, which is widely held to be about censorship, despite the Bradbury's statements that the book was about "the moronic influence of popular culture through local TV news".