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.
Updated 15 September 2026
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
UCP · 2026
Documents business profile discovery, checkout states, an order object and fulfilment and adjustment expectations.
Source checked 2026-09-13
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.
Source checked 2026-09-13