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Zero Data Retention

HTTP 451 UNAVAILABLE FOR LEGAL REASONS

Blocked because of a legal demand. 451 belongs to the 4xx client error class and is defined in RFC 7725.

Zero retention: your headers never leave this browser. Verify it yourself in DevTools.

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About HTTP 451

What Does HTTP 451 Unavailable For Legal Reasons Mean?

Blocked because of a legal demand. The code is registered with IANA and defined in RFC 7725.

Client error: the request has a problem, so it cannot be fulfilled as sent. Every code from 400 to 499 shares that general meaning, so a client that does not recognise 451 must treat it like 400.

When Do You See a 451 Response?

451 Unavailable For Legal Reasons, defined in RFC 7725, means access is denied because of a legal demand: a court order, a government block, a copyright takedown, or data protection rules applied by region. Some sites return it to visitors from jurisdictions they choose not to serve. The number is a nod to Ray Bradbury's novel Fahrenheit 451. It is more transparent than a generic 403 or 404.

How Do You Fix a 451?

Servers should explain in the body what legal demand applies and who made it, and may add a Link header with rel="blocked-by" naming the entity implementing the block. Clients cannot fix a 451 technically; the content is unavailable in that context. Operators should keep blocks narrowly scoped and documented, since overbroad geo-blocking also cuts off legitimate users.

What Does a 451 Response Look Like?

HTTP/1.1 451 Unavailable For Legal Reasons
Link: <https://isp.example.net>; rel="blocked-by"
Content-Type: text/html; charset=utf-8

451 is not cacheable by default: a browser or CDN stores it only when Cache-Control or Expires explicitly allows it.

To inspect a real one without sending it anywhere:

  1. Copy the response headers from your browser Network tab, or from curl -i.
  2. Paste them into the Header decoder to see every header explained.
  3. Check caching in the Cache lane.

Which Status Codes Are Related to 451?

  • 403 Forbidden: The server knows who you are and refuses anyway. Logging in again will not help.
  • 404 Not Found: Nothing at this URL, or the server will not say whether there is.
  • 410 Gone: Removed on purpose and not coming back. Search engines drop it faster than a 404.

Browse every code on the HTTP status codes page.

What Other Lanes Are in the Reference Section?

  • HTTP status codes: Every IANA-registered status code, with a page per code.
  • MIME types: File extensions to Content-Type, searchable both ways, plus a Content-Type parser.
  • HTTP methods: GET, POST, PUT, PATCH, DELETE and the rest: safe, idempotent, cacheable.

Elsewhere in 2http: Header decoder, Cookie decoder, Cache-Control decoder, CORS checker, User-agent parser, and all eleven lanes on the 2http home page. Part of the 2suite.io privacy-first ecosystem.

Frequently Asked Questions

Why is the code 451?

It references Fahrenheit 451, Ray Bradbury's novel about censorship, where books are burned. The number was chosen deliberately when RFC 7725 was written in 2016.

Is 451 cacheable?

Yes, by default caches may store a 451 response heuristically. Send explicit Cache-Control if the legal situation may change, so the block is not served longer than necessary.

Is HTTP 451 an error?

Yes. 451 is a client error response: the problem is in the request, so repeating it unchanged will usually fail again.

Is a 451 response cacheable by default?

No. Caches store a 451 only when Cache-Control or Expires explicitly allows it.

How Can You Verify That Nothing Leaves This Browser?

You do not have to take our word that your headers stay here. Developer tools show every request a page makes, so you can watch this page work and confirm that nothing is sent. The check takes under a minute.

  1. Open your browser developer tools with F12, or Cmd+Option+I on a Mac, and select the Network tab.
  2. Reload the page and let it finish. You will see the page's own files, its web fonts, and one anonymous page-view request. Nothing has been typed yet, so none of them can contain your headers.
  3. Click the clear icon in the Network tab so that the log is empty.
  4. Paste real headers into any lane and read the result.
  5. Look at the Network tab again. It is still empty. For extra proof, turn on offline mode after the page loads and every lane keeps working.

Only two things can add a line to that log, and neither carries your headers. Submitting the feedback form sends the vote and comment you typed. Typing characters in a script the page has not displayed yet, such as Cyrillic or Greek, can make the browser fetch the matching font file, and that request names only the font.

2http never sends a request on your behalf: the request builder writes code for you to run, and the meta inspector reads source you paste instead of fetching a URL. The production site also sends a Content-Security-Policy header that tells your browser to refuse connections to anywhere except this site and the anonymous analytics endpoint.

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