Meta-ExternalAgent: what it is, what it does with your content, and what blocking it costs
What Meta-ExternalAgent is
Meta-ExternalAgent collects pages to train future models. It does not decide whether Meta can cite you in an answer today — that is a different crawler with a different token. Blocking Meta-ExternalAgent is a decision about your content being learned from, not about your visibility.
Operator: Meta
robots.txt token: Meta-ExternalAgent
User-agent on the wire: meta-externalagent/1.1 (+https://developers.facebook.com/docs/sharing/webmasters/crawler)
Category: Model training
What blocking it actually costs
Your content is excluded from training Meta's Llama models and from Meta AI's corpus.
How to block Meta-ExternalAgent
Add this to your robots.txt:
User-agent: Meta-ExternalAgent
Disallow: /
The token must appear on its own User-agent: line. A named group replaces the User-agent: * group rather than adding to it, so anything you also want disallowed for this crawler has to be repeated inside its group.
How to allow Meta-ExternalAgent
User-agent: Meta-ExternalAgent
Allow: /
An explicit allow is worth writing even when you have no blanket block: it documents the decision, and it survives someone later adding a restrictive User-agent: * rule without thinking about AI crawlers.
robots.txt is not the only thing that can block it
A permissive robots.txt does not mean Meta-ExternalAgent can reach you. WAF rules, Cloudflare's bot-management settings, rate limits and country blocks all sit in front of robots.txt and answer first. A site whose robots.txt welcomes Meta-ExternalAgent and whose edge returns 403 to it is blocked in every way that matters — and nothing in robots.txt will tell you so.
This is the gap the AI Crawler Access Checker was built to close: it reads robots.txt and sends a real request carrying the crawler's user-agent, so you see what the crawler sees.
Official documentation
Meta documents Meta-ExternalAgent at https://developers.facebook.com/docs/sharing/webmasters/web-crawlers.
Common questions
- What user-agent does Meta-ExternalAgent send?
meta-externalagent/1.1 (+https://developers.facebook.com/docs/sharing/webmasters/crawler)- How do I block Meta-ExternalAgent?
Add a group to robots.txt naming the token exactly:
User-agent: Meta-ExternalAgent Disallow: /The group must name
Meta-ExternalAgenton its own line. AUser-agent: *group does not combine with a named one — under RFC 9309 the most specific matching group replaces the wildcard entirely, it does not inherit from it.- What does blocking Meta-ExternalAgent cost me?
Your content is excluded from training Meta's Llama models and from Meta AI's corpus.
- Can I tell a real Meta-ExternalAgent request from a fake one?
Not reliably. Meta does not publish verified IP ranges for Meta-ExternalAgent, so the user-agent string is the only signal, and anyone can send it. Treat robots.txt as a statement of policy rather than as enforcement.
Is Meta-ExternalAgent blocked on your site right now?
Reading your own robots.txt only answers half of it — a firewall rule can block Meta-ExternalAgent while robots.txt says it is welcome. The checker tests both.
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