Direct answer
Verify Another Agent's Work Before You Use It
Ask the other agent for its receipt IDs and check them at zambo.dev/verify before you rely on the output. An agent handing you a result is making a claim: this work ran, with these inputs, and produced this. A receipt ID turns that claim into something checkable in under a minute, and an agent that cannot produce one is telling you its work runs on trust alone.
Updated October 20, 2026.
Why agent-to-agent trust breaks
Agent chains fail quietly. Agent A summarizes a source it half read, Agent B builds on the summary, Agent C reports the result to a human as fact, and nobody in the chain can point to where a wrong step entered, because each handoff was prose. Prose handoffs have no check step: the receiver can believe the summary or redo the work, and believing is cheaper, so errors compound in the direction of confidence. Records break that pattern by giving the receiver a third option: check the record, then decide how much of the work still needs redoing.
Receipt IDs in handoffs
Make receipt IDs a standing part of every handoff you accept:
- Ask up front. Tell sending agents that results without receipt IDs will be treated as unverified drafts. That one rule changes what senders bother to record.
- One ID per step that matters. A multi-step job should arrive with the step receipts and the job-level record that binds them, so you can check the whole set, not just the final claim.
- IDs travel with the output. The receipt ID belongs in the handoff itself, next to the result it covers, the pattern Zambo handover uses: one link carries the whole job, and each step inside carries its own record.
The automated check
- Fetch each receipt. Open the receipt page or its JSON form and read the tool, the inputs on record, the saved result, and the date.
- Verify the record. Run the ID through zambo.dev/verify, or recompute the hashes in your own code for an automated pipeline. A match confirms the saved result was not changed after the fact.
- Compare against the claim. Check that the result in the record is the result you were handed, and that the steps on record cover the steps the sender claims. A missing step is work that, on the record, did not happen.
- Decide your reliance level. Checked steps can be built on. Unchecked or missing steps get redone, spot checked by hand, or flagged in your own handoff as unverified.
Provenance classes: what the record shows vs what it cannot
- Shown by the record: which tool ran, the inputs it received, the exact saved result, and when it ran, in a form that proves the saved result was not changed after the fact.
- Shown with one more step: that a real-world effect followed, when you read the effect back in its own system, for example a sent message visible in the sent folder.
- Not shown by any record: that the result was correct, that the right tool was chosen, or that the sender's summary of the result is fair. Those stay judgment calls, and the record's job is to make them informed ones.
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Honest limits
Verification checks records, not intentions: an agent can record a call faithfully and still have called the wrong tool or misread the result, and the receipt will verify cleanly because the record is honest about what ran. Receipts also only cover work that ran through a recording layer; anything the other agent did outside it arrives with no record and should be treated as unverified, however confident the summary sounds.
Frequently asked questions
How do I verify another agent's work?
Ask the sending agent for the receipt IDs covering its work, then check each ID at zambo.dev/verify before relying on the output. Compare the saved result in each receipt with the result you were handed, and confirm the steps on record cover the steps claimed. Anything without a receipt is unverified, so redo it, spot check it, or flag it as unverified in your own handoff.
What does a receipt check actually prove?
A receipt check proves the saved result was not changed after the fact: the result in the record is the result that came back when the call ran, produced by the tool on record with the inputs on record at the recorded time. It does not prove the result was correct or that the right tool was chosen, which remain judgment calls for the receiver.
What if the other agent has no receipts?
Then its work runs on trust alone, and you should price that in: treat the output as an unverified draft, redo the steps that matter, or route the work through a recording layer such as the Zambo MCP so the next run leaves receipts as it goes. An agent that routinely produces no records is a process problem, not a prompting problem.
Can verification be automated between agents?
Yes. Receipts are public pages with a JSON form, so a receiving agent or pipeline can fetch them, recompute the record checks in code, and compare saved results against handed-over outputs without a human in the loop. The free verifier at zambo.dev/verify runs the same checks in a browser for one-off human review.
How do receipts fit into a handover between agents?
The handover carries the job, steps, outputs, and open items as one record, and each step inside it carries its own receipt ID. The receiver accepts or flags the handover after checking the records, so gaps surface at the handoff instead of later. Zambo handover at zambo.dev/handover is built on exactly this pattern.