# Commerce protocol

A shared message and state contract for selected buyer, seller or platform interactions, typically covering how a checkout is formed, updated and turned into a merchant order.

Source: https://aecon.ai/glossary/commerce-protocol
Updated: 2026-09-15

## In practice

An agent creates a checkout against a merchant's endpoint, compares the returned total with the amount its principal approved, and completes it once — producing an order the merchant's own systems own.

## The distinction

A commerce protocol carries part of the transaction, not the commercial relationship. A completed checkout is not settled payment, settled payment is not delivered work, and delivered work is not accepted work.

## The transaction is being divided

No single specification covers offer through accepted work. Each one preserves the position of the party that wrote it.

| Component | What it natively carries |
| --- | --- |
| UCP and ACP | Checkout and order state, held by the seller |
| AP2 | Signed intent, checkout and payment mandates |
| x402 and MPP | A machine-readable payment request and receipt |
| Card, bank and wallet components | The credential and the rail |

None of them defines who accepts the delivered work. That absence is the seam worth watching, because acceptance is where the buyer's value actually sits.

## Same word, different meaning

Similar field names do not prove interoperable semantics. UCP's `completed` checkout means the business reports the order was placed, not that funds settled or work was accepted. UCP's `complete_in_progress` can contain no order at all, so a lost response cannot justify a second completion attempt.

Before treating two components as interoperable, pin the version or commit, the actor roles, the identifier rules and what happens when a field changes or a callback disappears.

## The practical decision

The question is not which protocol will own agentic commerce. It is which component carries the state you need, which system stays authoritative at the next hand-off, and how you reconstruct one order when those systems disagree.

## Sources & context

- [Universal Commerce Protocol specification](https://ucp.dev/specification/overview/) — UCP, 2026. Documents business profile discovery, checkout states, an order object and fulfilment and adjustment expectations. Checked 2026-09-13.
- [Agentic Commerce Protocol](https://github.com/agentic-commerce-protocol/agentic-commerce-protocol) — Agentic Commerce Protocol, Stable 2026-04-17. Documents a merchant-owned create, retrieve, update, complete and cancel checkout plus signed order webhooks; settlement, returns, tax and acceptance sit outside it. Checked 2026-09-13.

## Related reading

- [Agentic commerce](https://aecon.ai/glossary/agentic-commerce)
- [Mandate](https://aecon.ai/glossary/mandate)
- [Settlement](https://aecon.ai/glossary/settlement)
- [Merchant of record (MoR)](https://aecon.ai/glossary/merchant-of-record)