Did My Agent Lie? The Quick Receipt Check

Last updated: 2026-09-25

Your agent says the task is done. Here is how to check instead of arguing with the transcript. The method: each executed tool call through Zambo returns a verifiable execution receipt. A planned or preview result is not an execution-success receipt. No receipt, no proof. Three checks settle it.

Check 1: Ask for the receipt ID

"Done" is not an artifact. Ask the agent for the receipt ID of the call. If it cannot produce one, the work is unverified.

Check 2: Open the receipt and compare the hash

Open the receipt at its public page. Compare the result summary and the result hash against what the agent claimed. The sha256 hash means any alteration after the fact breaks the match.

Check 3: Check the timestamp

The receipt carries a timestamp. If it is from before you asked, or from a different session, the agent is citing old or borrowed work.

Make every future call checkable

Route tool calls through the Zambo MCP endpoint with a stable session id, as in the install guide. Then checks 1 through 3 apply to each executed call that returns a receipt.

Try it now (paste and run)

SESSION_ID="recipe-lie-check-$(date -u +%Y%m%dT%H%M%SZ)-$$"; curl -fsS --max-time 45 -w '\nHTTP %{http_code}\n' https://zambo.dev/api/mcp -H 'Content-Type: application/json' -H 'Accept: application/json, text/event-stream' --data-raw "{\"jsonrpc\":\"2.0\",\"id\":\"recipe-check\",\"method\":\"tools/call\",\"params\":{\"name\":\"zambo_universal\",\"arguments\":{\"need\":\"Find the current ETH/USD price from a read-only source and return the source.\",\"_session_id\":\"$SESSION_ID\"}}}"

Open the returned receipt id at https://zambo.dev/run/<receipt-id> and confirm its result hash matches the tool output.

Frequently asked questions

What if my agent used a different tool?

Then there is no Zambo receipt for that call. The check covers calls that went through the receipting endpoint. That is the point.

Can a receipt be faked?

The receipt is minted by the server at execution time with a hash of the actual arguments and result. Altering it breaks the hash.

Does this cost anything?

No. 20 calls per tool per day are free with no account.

Where do I verify?

At https://zambo.dev/verify or at any https://zambo.dev/run/ receipt page, using the receipt id.

Try Zambo

Run your first verified call at https://zambo.dev/install/ and check any receipt at https://zambo.dev/verify.