Meta-ExternalFetcher: what it is, what it does with your content, and what blocking it costs
What Meta-ExternalFetcher is
Meta-ExternalFetcher fetches a page because a person asked for it — they pasted your URL, or followed a link, and asked the assistant to read it. There is no crawl schedule and no training corpus involved. Blocking it means failing a visitor who explicitly asked for your page.
Operator: Meta
robots.txt token: Meta-ExternalFetcher
User-agent on the wire: not published by the operator
Category: User-triggered fetch
What blocking it actually costs
Meta AI cannot fetch your page when a user asks about a specific link.
How to block Meta-ExternalFetcher
Add this to your robots.txt:
User-agent: Meta-ExternalFetcher
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-ExternalFetcher
User-agent: Meta-ExternalFetcher
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-ExternalFetcher 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-ExternalFetcher 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-ExternalFetcher at https://developers.facebook.com/docs/sharing/webmasters/web-crawlers.
Common questions
- What user-agent does Meta-ExternalFetcher send?
Meta does not publish an exact user-agent string for Meta-ExternalFetcher. Match on the
Meta-ExternalFetchertoken in robots.txt rather than on a full string you found elsewhere.- How do I block Meta-ExternalFetcher?
Add a group to robots.txt naming the token exactly:
User-agent: Meta-ExternalFetcher Disallow: /The group must name
Meta-ExternalFetcheron 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-ExternalFetcher cost me?
Meta AI cannot fetch your page when a user asks about a specific link.
- Can I tell a real Meta-ExternalFetcher request from a fake one?
Not reliably. Meta does not publish verified IP ranges for Meta-ExternalFetcher, 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-ExternalFetcher blocked on your site right now?
Reading your own robots.txt only answers half of it — a firewall rule can block Meta-ExternalFetcher while robots.txt says it is welcome. The checker tests both.
Check your site free