While browsing the internet in the coming months you may encounter error code 451, a new XML specification that will inform users when content has been blocked for legal reasons.

We should all be familiar with error code 404 which presents itself when attempting to navigate to a page which cannot be found. The problem was that sometimes that site was blocked because the content was illegal in your country, this was however, never made clear.

This new error code would serve to alert users to the fact that the site they are attempting to view has been blocked, be it by an internet service provider or the authorities.

There is however a catch, developers will need to implement the error code so that websites can actually warn you that content has been blocked. In addition to this content will need to be labelled as blocked, for the error code to trigger.

Mark Nottingham, Chairman of the IETF HTTP Working Group explained the problems associated with this in a blog post. “By its nature, you can’t guarantee that all attempts to censor content will be conveniently labeled by the censor”.


As Nottingham explains, error code 451 is a great tool through which to alert users that a website has been restricted by somebody and can help draw attention to censorship especially if it is coming from the state.

Nottingham concluded by saying, “In some jurisdictions, I suspect that censorious governments will disallow the use of 451, to hide what they’re doing. 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.”

[Source – The Verge] [Image CC by 2.0 – Cory Doctorow]