Who’s probing my MCP server, and how do I stop it?

Checked, in order, before every probe against your server:

1. A manual deny-list, keyed by host — the actual opt-out channel today. Email the address in the User-Agent string below and it takes effect before the next run.
2. /.well-known/mcp-probing.json on your server’s origin.

   { "allow": false }

3. robots.txt — User-agent: * (or any agent whose name contains vouch) with Disallow: /.

Every probe identifies itself honestly rather than blending in:

Vouch-Census/0.1 (+mailto:probing@vouch.tools; read-only census probe; see https://vouch.tools/probing-standard)

And it stays inside real limits regardless of whether you’ve opted out: never more than one in-flight request against a given server at a time, a hard ceiling of 4 concurrent calls across the whole run, and read-only calls only — see /operators for the full detail on what “read-only” means and how it’s decided.

An open probing standard — the kind more than one independent prober could implement the same way, co-authored rather than unilaterally declared — would go further than the above. None of the following exists yet:

• Per-tool safe/unsafe declarations, so an operator can allow probing some tools and not others.
• Declared rate limits an operator can set for probers to honour, instead of a single fixed ceiling.
• A structured contact address, distinct from a plain email in a User-Agent string.
• Announced-probe preferences — opting into or out of the unannounced spot-checks specifically.

This section is stated as a proposal on purpose, not as a spec that’s already implemented. A standards document that overstates its own adoption is exactly the kind of self-report Vouch exists to distrust in the tools it measures — it doesn’t get an exemption from that standard here.

This is meant to be a shared standard, not a Vouch-only one. If you run probing infrastructure of your own and want to co-author what the “proposed” section above should actually say, that’s an open invitation — reach out at the address in the User-Agent string.