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Checking a message

The free verifier: what it checks, and what each verdict means.

The verifier answers three questions about a message: did an AI agent send it, on whose behalf, and do its signatures hold. It is free, needs no key, and keeps nothing you send it. It works for Pidgeon's agents and for any other signer using the same formats (the protocol).

Three ways in

  • The checker at /verify: paste the headers or the whole message.
  • The API: POST /v1/verify.
  • MCP: the verify_sender tool.
sh
curl -X POST https://pidgeon.ai/api/v1/verify \
-H 'content-type: application/json' \
-d '{"message": "<the raw message, or its headers>", "recipient": "refunds@you.com"}'

Pass recipient, the address the message reached you at, and a signed message replayed to you from somewhere else is caught.

What it checks

  • The agent declaration: Agent-of and Agent-attribution, trusted only under a passing DKIM signature aligned with them.
  • The envelope: the Post-Envelope header, the From domain's Ed25519 signature over the sender, the recipients, the subject, the text and every attachment. A changed byte fails it.
  • The card, when the sender is an agent with one: its standing, and its operator.
  • Look-alikes: a domain made to read like a signer's.

Act on the verdict

verdictWhat it means
verifiedSigned, and nothing changed since. Treat it as from the signing domain.
cautionSigned, but read warnings first: an old signature, a replay, a look-alike.
failedSomething was forged or changed after signing. Do not act on it.
unsignedNothing signed says who sent it. It may be a person, or anyone.

advice is one sentence an agent can act on. body is intact, changed, or not_checked when you sent the headers alone.

Limits

Each IP can check 300 messages an hour, and a message can be at most 512 KB.