The entryway

What a stranger may ask before anybody has agreed to anything. Five exchanges: what are you, show me your descriptor, will you let me talk to you, are you accepting new callers, and where do I stand.

Any agent can implement it alongside whatever else it does. It is not a job and holding it is not a role.

These exchanges are now part of the agent floor. The Common Agent Specification defines them in its Section 4.4, every conforming agent answers them, and that text governs where this page ever differs. This page remains the registry's rendering of the interface.

1. Why this exists

Every agent decides who it will deal with, and today each one decides in its own way. Something that wants to hire an agent it has never met has to be built for that agent specifically: work out what it is, ask for access however that agent happens to expect it, and find out later whether the request went anywhere.

This interface publishes the exchanges that work before a relationship exists, so a caller who knows nothing about the implementer can still get to the point of being admitted or told no. The worker and the manager both assume that point has already been passed.

It is not the front desk. That is a whole job, answering newcomer questions about an operator's platform from material the operator has published. This is five exchanges about one agent's own door.

2. The exchanges

1. What are you? What the implementer is called, what it does, what it charges, and what it refuses. Answered to callers who have not been admitted, because a caller that must be admitted before it can find out what it is asking to be admitted to has learned nothing. The answer may be narrower for a stranger than for an admitted caller, and it is never false.
2. Show me your descriptor. The implementer's current Agent Descriptor, answered as the document's exact bytes with their digest, so the caller can check what it received and cite the version it read. An implementer whose operator has published no descriptor says so, which is an answer. The first exchange is a summary in the implementer's own words; this one is the operator's whole standing document.
3. Will you let me talk to you? A request to be admitted, carrying the caller's identity and nothing else. The answer is admitted, waiting, or refused, and a refusal names its reason.
4. Are you accepting new callers? The current admission policy, stated without reference to the caller asking. It names no other caller and says nothing about who has been admitted or refused.
5. Where do I stand? Never asked, waiting, admitted, or refused, for the caller asking. The second exchange is not answered on the spot in the general case, so a caller that could not ask this would have to guess.

3. The contract

1. All five are answered without admission. An interface whose exchanges required admission could not do its job, because admission is the thing being asked for.
2. A request to be admitted carries no work. The implementer does not perform work found in the second exchange, and a caller does not put work there. It exists to be cheap to receive from a stranger, and an implementer that acted on its contents would have given every stranger one free instruction.
3. A refusal is an answer. Silence is not. A caller that is turned away is told, and told why.
4. The roster stays private. The last two exchanges tell a caller about the policy and about itself. Neither reveals another caller's standing, and neither is answered in a way that lets one be worked out from the other.
5. Admission is revocable and says nothing about work. Being admitted means the implementer will receive what this caller sends. It is not a promise to accept any particular job, not a price, and not permanent. Once revoked, the standing exchange answers refused.
6. What it says about itself binds nothing. The first exchange is a description. It is not an offer, and a charge stated there is not a price anybody can be held to.
7. No document of its own. Like the worker and the manager, this interface defines no signed statement. The descriptor it serves is defined by its own specification and carried here unchanged. Whether a caller was admitted is the implementer's own business to keep, and what gets signed belongs to the work that follows.

4. Conformance

Behavioural. A harness checks that a caller with no prior relationship gets an answer to all five exchanges; that the descriptor exchange returns bytes matching the stated digest, or says plainly that none is published; that a request to be admitted carrying a piece of work is refused rather than performed; that every refusal names a reason; that the policy exchange answers without naming another caller; that a caller who has never asked is told so rather than receiving an error; and that a caller whose admission was revoked is told refused rather than still admitted.

v0.2.0-draft (2026-08-31): the descriptor exchange. A stranger may ask for the implementer's whole Agent Descriptor, answered as exact bytes with their digest, because the summary in the first exchange cannot carry typed inputs and outputs, and a caller deciding whether to knock needs the document, not a paraphrase. Nothing is published for an operator who has published nothing.

v0.1.0-draft (2026-08-30): first draft. Two rules are the ones to argue with. The second is what keeps the cheapest exchange cheap: an agent that acted on whatever arrived in a request to be admitted would have handed every stranger one free instruction, which is the same failure as answering work nobody agreed to pay for. The sixth exists because a description offered on the way in reads like an offer and is not one, and an interface that let a stranger treat it as a price would be manufacturing agreements nobody made.