451

Unavailable For Legal Reasons

4xx Client Error

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ELI5

This content is blocked by law or legal restrictions in your area. It's like a book that's banned in your country.

Server perspective

Use 451 when a legal demand prevents the resource from being provided.

When to use

  • •Return 451 for legally compelled blocks, takedowns, or jurisdiction-specific denials
  • •Use it when the denial is specifically legal in nature rather than a generic policy decision
  • •Government censorship or takedown requests
  • •Court-ordered content removal
  • •Geographic legal restrictions
  • •Copyright-related content blocking
  • •Regulatory compliance blocking

How to respond

  • •Include a human-readable explanation in the response body
  • •Optionally include Link with rel="blocked-by" to identify the entity implementing the block

Headers to consider

  • •Link

Response body

  • •Include a concise legal-block explanation and safe metadata about the restriction when appropriate.

Server-side pitfalls

  • •Do not use 451 for ordinary company policy or permission denials; use 403 instead
  • •Do not use the blocked-by Link relation to identify the legal demander when the body should explain that context
  • •General access denied (use 403 Forbidden)
  • •Resource doesn't exist (use 404 Not Found)
  • •Company policy restrictions (use 403 Forbidden)
  • •Authentication required (use 401 Unauthorized)

Examples

Government content blocking

Request:GET https://api.example.test/political-content
Response:451 Unavailable For Legal Reasons # Headers Content-Type: application/json Link: <https://spqr.example.org/legislation>; rel="blocked-by" # Body { "error": "unavailable_for_legal_reasons" }

Content blocked due to government censorship laws

DMCA copyright takedown

Request:GET https://api.example.test/copyrighted-video
Response:451 Unavailable For Legal Reasons # Headers Content-Type: application/json # Body { "error": "unavailable_for_legal_reasons" }

Content removed due to copyright infringement claim

References

Related Status Codes

403

Forbidden

I know who you are, but you're not allowed to do this. You don't have permission for this action.

404

Not Found

The thing you're looking for doesn't exist here. It's like knocking on a door and nobody's home.