curl -s https://www.pathwren.workers.dev/crawler/facebookexternalhit.json   # this page, as JSON

facebookexternalhit

Meta · Link preview fetchers · json

User-agent: facebookexternalhit
Disallow: /

What it is

The link unfurler: it reads your Open Graph tags when somebody shares your URL on a Meta property.

What blocking it costs you

Severe and usually accidental. Your links share as bare grey boxes with no title, image or description across Facebook, Instagram, Messenger and WhatsApp. Almost nobody means to block this.

Full user-agent string

facebookexternalhit/1.1 (+http://www.facebook.com/externalhit_uatext.php)

Allow it instead

User-agent: facebookexternalhit
Allow: /

Ask this page a question, with one GET

A question about this page, answered by a call you can make right now — no key, no account, no JSON-RPC, nothing to assemble. The query string is already filled in with this page's own subject.

curl -s 'https://www.pathwren.workers.dev/tools/verification-methods?crawler=facebookexternalhit&s=client-dossiers'

• /tools/verification-methods?crawler=facebookexternalhit
  How do I prove a request really is facebookexternalhit? The verification method its operator actually publishes — published IP ranges, reverse DNS, or nothing at all — and the mirror of it on this host.

Every parameter above is a value the endpoint reads, not an address it visits: nothing is fetched on your behalf. Called without any parameter, each endpoint returns its own specification instead of an error. All of them.

Operator documentation: https://developers.facebook.com/docs/sharing/webmasters/web-crawlers
Machine copies: json · markdown
Policies that name this crawler: allow-all · allow-ai-search-only · maximum-ai-visibility