What A2A carries
A2A, the Agent2Agent protocol, is how agents talk to each other across vendors: one agent discovers another's capabilities through its agent card, sends a task, and the task moves through states (submitted, working, completed, failed) carrying messages and artifacts, the files and outputs the work produces. That transport is real and useful: it is how a job crosses from one agent's runtime into another's.
What A2A does not carry is a checkable record of the work itself. A completed task state is the receiving agent's own report. The artifacts arrive as content, not as evidence: nothing in the exchange lets a third party recompute whether the result handed over is the result that was actually produced, or whether it was edited on the way.
What an AER-1 handover receipt adds
- A receipt per finished step: each completed step of the job carries its own AER-1 receipt, the record of that tool call with its saved bytes and sha-256 digest, so the receiver checks the work, not the summary of the work.
- A package, not a pile: the handover gathers the goal, the steps, the outputs, and the open items into one link the receiver opens and works from.
- A decision with its own receipt: when the receiver accepts the handover or flags a problem with it, that decision is recorded as a receipt too, so the acceptance itself cannot be quietly rewritten later.
- A chain the next agent can continue: because the record is portable, the receiving agent can pick the job up and keep going, in a different AI entirely, with the earlier steps still checkable.
The definition underneath all of it: an agent receipt is a record of one ai agent tool call that anyone can check: it keeps the exact saved bytes and their sha-256 digest, and it proves the result was not changed since it was saved, not that it was right.
The flow, concretely
- Agent A finishes a job through Zambo's tools; every call leaves a receipt.
- Agent A hands the job over: one handover link carrying the goal, steps, outputs, and receipts.
- Agent B (or a client) opens the link, checks any step's receipt free at zambo.dev/verify or offline with the Python verifier, and accepts or flags it.
- The acceptance is recorded, and Agent B continues the work with its own receipts joining the same job.
HANDOVER is Zambo's flagship product, and this is the shape it takes between agents: A2A moves the conversation, the handover receipt moves the proof. Set it up at zambo.dev/add: 20 free calls per day to start, then the $0.99 Day Pass for 24 hours or the Zambo Pass at $29 for 30 days, one payment.
Frequently asked questions
What does A2A carry between agents?
A2A carries the conversation and the task: capability discovery through agent cards, task state as the job moves from submitted to completed, the messages exchanged, and artifacts, the outputs the work produced. It is a transport protocol for agent-to-agent work.
What does an AER-1 handover receipt add to an A2A handoff?
Evidence. Each finished step carries an AER-1 receipt, the checkable record of that tool call, and the receiver's accept or flag decision gets its own receipt. A2A moves the work; the handover receipt lets the receiver, or any third party, check that the work handed over is the work that was done.
Can the receiver check the work without a Zambo account?
Yes. Every receipt is a public page, and checking one is free at zambo.dev/verify with no account. The offline verifiers, aer-1 on npm and aer1-verify on PyPI, check the same record with no network at all.
What is an agent receipt?
An agent receipt is a record of one ai agent tool call that anyone can check: it keeps the exact saved bytes and their sha-256 digest, and it proves the result was not changed since it was saved, not that it was right.
Does the receiving agent have to use Zambo to continue the job?
To continue the same job record, yes: the receiving agent connects to the same Zambo endpoint, https://zambo.dev/mcp, accepts the handover, and its own calls join the chain. Checking the existing record needs nothing: the receipts are public and free to verify from anywhere.