Also called: verifier, verification profile
In plain words
A verifier profile is the rulebook for one action. It says which parameters a claim must carry, what to read at the destination, the exact comparison that counts as a match, and two time windows: a tolerance (how late is still on time) and a deadline (when to stop looking). A verifier is the code that implements a profile.
Publishing the profile matters. If the rules for "verified" are secret, a verdict is just an opinion; if they're public and versioned, anyone can see what was checked and argue with it.
How QED Proof uses it
Every action has a profile named by an id and version, and each receipt records which one produced it (observation.verifier). Verdicts are decided deterministically from the claim, the facts and the profile's match rules. A language model may help turn free text into a structured claim, but it never decides a verdict.
Verifiers are open source as part of Proof of Agent Work. At trust level 3, planned and not built yet, a receipt will also carry the code_hash of the exact verifier build that ran.
Example
github.commit.push v1 has a tolerance of 10 minutes and a deadline of 15: a commit that appears on the branch within 10 minutes of the claim is verified, between 10 and 15 is late, and still absent at 15 is failed. github.checks.pass allows an hour, with a two-hour deadline, because CI takes longer.