Testing an AI shopping agent's checkout flow? There's no sandbox for that yet — so I built one

If you're building or evaluating an AI agent that can shop and check out on its own, you've probably run into the new "agentic commerce" protocols: ACP (OpenAI + Stripe + Meta), AP2 (Google), and UCP. They define how an agent talks to a merchant to create a checkout session, apply a payment token, and get an order back.

Stripe's own test mode covers the payment half fine — test cards, test API keys. But there's no hosted "fake merchant" you can point your agent at to verify the protocol half: does your agent correctly create a session, handle a 422 idempotency conflict, parse the order response, retry politely? You either mock it yourself from the spec, or risk finding out against a real merchant.

So I built acp-sandbox — a small hosted mock merchant implementing the ACP checkout API, live at https://acp-sandbox.flo-voice1.com.

What it does

It implements the real checkout_sessions lifecycle from ACP's 2026-04-17 spec: create, retrieve, update, complete, cancel. Responses match the actual CheckoutSession/Order/Error schemas for the fields it supports — I pulled the OpenAPI spec directly rather than guessing field names.