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Guide · 11 November 2026

What does HTTP 451 Unavailable For Legal Reasons mean?

HTTP status 451 means that the server answering the request refuses it because of a legal demand. It is sent by sites that shut out visitors from some countries themselves, and by services in front of a site, such as a CDN acting on a legal order. Provider blocks that act in DNS or on the connection never reach your server, so the visitor sees a notice page, a browser security error or a connection error instead.

Source: IETF RFC 7725, February 2016

What does RFC 7725 say a 451 should contain?

RFC 7725, written by Tim Bray and published in February 2016, defines 451 as the server "denying access to the resource as a consequence of a legal demand". The rules are short:

The RFC also says the server sending it might not be the origin server, and names ISPs, cache providers and DNS servers among those that can block. MDN's reference page carries the example response from the RFC, and points to Fahrenheit 451 as the source of the number; the RFC itself ends with "Thanks also to Ray Bradbury."

HTTP/1.1 451 Unavailable For Legal Reasons
Link: <https://spqr.example.org/legislatione>; rel="blocked-by"
Content-Type: text/html

Sources: IETF RFC 7725, February 2016 · MDN, 451 Unavailable For Legal Reasons, last modified 4 July 2025

Who actually sends a 451?

A site restricting itself. When the GDPR took effect in 2018, many US news sites chose to block visitors from Europe rather than comply. Nieman Lab reported on 7 August 2018 that more than 1,000 news sites were still unavailable in the EU, including sites run by Tronc, Lee Enterprises and GateHouse Media. Nieman Lab does not say which status code they sent. In March 2021 the GDELT Project wrote that 451 errors had come from around 560 news outlets, mostly small local US ones, only in its crawlers located in EU member countries, and that most of these sites shared hosting platforms that likely applied the block for them.

Sources: Nieman Lab, 7 August 2018 · GDELT Project, 25 March 2021

A CDN in front of the site. In July 2025, Cloudflare began showing "Error 451" for some pirate sites to visitors in the United Kingdom, with a notice saying that in response to a legal order it had limited access to the site through its pass-through security and CDN services within the UK.

Source: TorrentFreak, 15 July 2025

Why do most provider blocks not show a 451?

Because most provider blocks stop the visitor before any web server is asked. In Germany, the CUII's blocks are DNS blocks: the providers' DNS servers, which turn a domain into a server address, send visitors of a blocked domain to an information page; in our own measurements in November 2026, some answer that the domain does not exist instead. In Poland, operators apply the CERT Polska warning list by replacing the address in the DNS answer with the address of a warning page. Nothing here produces a status code from your server, and your server logs stay empty.

On an https site, the redirect usually does not even show the notice. A browser sent to a notice server expects your certificate and gets someone else's. In our own measurements in Germany in November 2026, a visitor sent to a notice server over https usually saw a browser security error, not the notice. Other provider blocks cut or drop the connection, and the browser shows a connection error. A 451 from a provider is possible under RFC 7725.

Sources: heise online, 16 July 2025 · CERT Polska, Lista Ostrzeżeń, checked 11 November 2026

What happens in Google Search if your site sends 451?

Google treats every 4xx status other than 429 the same way: it does not index the URL and removes it from the index if it was there. Googlebot's default addresses appear to be based in the USA, and Google asks sites to treat Googlebot like any other visitor from the country it appears to come from. So a 451 for US visitors is also a 451 for Googlebot's default crawler, and those pages drop out of search.

Sources: Google Search Central, HTTP status codes · Google Search Central, locale-adaptive pages; both checked 11 November 2026

How do you find out who sent the 451?

  1. Read the whole response, not only the code. A Link: ...; rel="blocked-by" header names whoever applied the block. The body should name the order and the authority; Cloudflare's UK page links to an entry in the Lumen Database.
  2. Check your origin logs. If your server logged the request and answered 451, the rule is yours: a geo rule in your code, your hosting platform or your firewall. If your server never saw the request, the 451 came from something in front of it: your CDN acting on an order, or a geo rule you set at the CDN yourself.
  3. Check from the visitor's network. A CDN's legal block can be limited to one country: Cloudflare's UK 451 applies within the United Kingdom only. A test from a datacenter elsewhere will not show it; see why datacenter monitors miss ISP blocks.

If you send 451 yourself, follow the RFC: say in the body which law you are applying and to whom, and add a blocked-by link that identifies you. A support agent reading "451" with no text has nothing to tell the customer.

How linkspect reports a 451

linkspect opens your URL through real customers' connections of named providers in Germany, Poland and Norway, and separates who stopped the page. A provider's or CDN's block page shown instead of yours is reported as blocked, with the place it happened: a CDN's own block page (for example Cloudflare's 451 page for a legal order) or a provider page. A 451 or other refusal from your own site, because of your geo or legal rules, is reported as your site refusing us, not as a block, and it stays free once billing starts. Provider DNS blocks are reported with how they work, for example a redirect to a notice page; see the verdict reference. Get early access or read the API quickstart.