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The Quickstart replays a bundled fixture. This is a real run: an agent pays two APIs, haia-trace assembles the receipts, and the agent reads its own verdict and stops spending.

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Run it

Three steps — record, assemble, act:
The middle step is Trace. The other two are the agent — which is the whole point: recording and assembling are separate from the payment, and nothing in the payment path waits on them.

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1. The agent pays

Two paid calls. The first settles. The second is signed, sent, and never comes back with a settlement — the agent is left holding a payment it cannot account for. It records as it goes, to a run file it owns.
Terminal recording of node buyer.mjs: the traced agent pays two APIs, the second returning no settlement, and writes the run to .trace/events.

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2. haia-trace build assembles the receipts

The agent has already exited. This step reads the evidence it left behind — one Receipt per operation — and could just as well run on another machine.
Terminal recording of haia-trace build: two receipts assembled from nine events, op-1 FULL and op-2 PARTIAL with an observed fault and a missing settlement.
op-2 is the point. A signed authorization left the agent and nothing came back to say what became of it. The agent cannot tell a payment that never settled from one that settled silently — so instead of guessing either way, the receipt names the milestone that stayed open and records the fault it saw.

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3. The agent acts on the verdict

completeness and missing are read by a machine, with no human in the loop. The process exits non-zero, so the same file works unchanged as a CI gate.
Terminal recording of node policy.mjs: op-1 is complete and safe to continue, op-2 is partial and stops the spend chain, exit status 1.
The money and the sellers are simulated — there is no chain, no facilitator and no wallet. Everything between the hook firing and the verdict is the shipped code path: the @x402/core client, its hooks, the recorder, the events on disk, and the assembler. This example fakes the payment, never the trace.

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The same recorder in a full application

arc-nanopayments is a complete app — gasless USDC nanopayments on Arc, with an autonomous buyer agent, a Next.js seller and a dashboard. It traces both sides of the payment, and attaches to Circle’s @circle-fin/x402-batching rather than @x402/core: the same one-line attach against another SDK’s hooks.

The buyer

agent.mts — the agent attaches to its GatewayClient and records as arc-nanopayments-buyer.

The seller

lib/x402.ts — the paywalled routes attach to the gateway middleware and record as arc-nanopayments-seller.
Its dashboard reads the run files straight back off disk and renders a payment timeline — the recorded events, not assembled Receipts. The app never has to ask anyone for its own evidence. Live at arc-nanopayments.gdev.haust.app — it opens on a sign-in screen, and the account is in the repository’s Demo Credentials. A second app, arc-escrow — an end-to-end escrow workflow on Arc — is still being built and is not traced yet.

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Next steps

Connect x402

The one-line attach, what gets recorded, and what never does.

What a Receipt is

Stages, evidence, missing, exceptions — the model behind the verdict.

See all three roles

The buyer’s, the seller’s and the facilitator’s view of one payment.

CLI reference

Every command, flag, and the .trace/ layout.