Verify a Claude Code Session with Receipts

Last updated: 2026-09-25

Claude Code can do real work in your terminal, but its transcript is not proof. This recipe shows you how to run the session's tool calls through Zambo so each executed call returns a verifiable execution receipt: a public record with the tool name, an arguments hash, a timestamp, a result hash, and a lookup ID. A planned or preview result is not an execution-success receipt. When the session ends, you verify the receipts instead of trusting the transcript. Free tier, 20 calls per tool per day, no account.

The recipe

  1. Connect. Add the Zambo MCP server to Claude Code using the config at the install guide.
  2. Work under one session id. Keep a stable session id for the whole task so every receipt chains to the same session.
  3. Call tools through the server. Use capability search to find the right specialist tool, then call it with your exact task.
  4. Collect receipt IDs. Each executed tool call returns a receipt id. Save them as the session runs.
  5. Verify. Open each execution receipt at its public receipt page and check the result hash and the timestamp against what the session claimed.

Try it now (paste and run)

SESSION_ID="recipe-claude-$(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 BTC/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

Do I need an account?

No. The free tier is 20 calls per tool per day with no account.

What does a receipt prove?

That the tool ran with those arguments at that time and returned that result. The hash lets anyone detect whether the record was altered after the fact.

What if the tool call failed?

Failed lookups still mint truthful receipts. The receipt records the failure instead of pretending the call succeeded.

Can someone else verify my receipt?

Yes. Anyone with the receipt ID can open the public receipt page. No account and no permission needed.

Related guides

Try Zambo

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