ACP Example

Minimal implementation of the Agentic Commerce Protocol (ACP) — spec version 2026-01-30.

Built to understand ACP from the inside. Implements both sides: a merchant server and an agent client.

Spec currency. This tracks 2026-01-30. Upstream has since published 2026-04-17, and this example has not been updated to it. What that version adds and this does not implement:

• 3-D Secure results — an authentication_result carrying outcome plus three_ds_cryptogram, electronic_commerce_indicator, transaction_id and version. Note the client here already advertises capabilities.interventions.supported: ["3ds"], so against 2026-04-17 it claims a capability whose result shape the server does not produce.
• Out-of-stock sessions — a checkout session state for unavailable items.
• display_name on payment handlers.

2026-04-17 also drops authentication_metadata.channel.browser.* (the browser-fingerprinting block). This example never implemented it, so nothing here is stale in that direction.

Everything below is accurate for 2026-01-30. Treat it as a reading of that version, not as a current-spec reference.

What's here

• src/server.ts — ACP merchant (TicketShop), selling TOKEN2049 VIP passes
• src/client.ts — AI agent that buys a ticket via the full ACP checkout flow
• src/types.ts — ACP types (CheckoutSession, Allowance, etc.)
• OBSERVATIONS.md — What we learned implementing this from scratch

Run it

npm install

# Terminal 1: start the merchant server
npm run server

# Terminal 2: run the agent
npm run client

The agent creates a session, adds fulfillment details, gets a delegate payment token (with Allowance constraints), and completes the checkout.

Key observations

See OBSERVATIONS.md for the full findings. The most important:

The cross-merchant budget gap. ACP's Allowance is scoped to a single merchant_id + checkout_session_id. An agent with a $500 budget buying at 3 merchants gets 3 independent Allowances. Total spend is tracked nowhere. This is a structural gap in every commerce protocol — not just ACP.

Protocol

ACP is a REST protocol (no MCP binding). Agents call merchant endpoints directly via HTTP with API-Version and Idempotency-Key headers.

Compare with ucp-example for the MCP-native transport version.