UCP: How Do Platforms and Merchants Coordinate Agent Commerce?

A shopping agent looks for a backpack across merchants with different product, shipping, checkout and payment interfaces. Building a separate integration for each can become expensive. The Universal Commerce Protocol (UCP) aims to make commercial capabilities discoverable and negotiable so platforms and merchants can identify what they both support.

The backpack example is hypothetical. This interprets official documentation; it does not verify any merchant’s support. Sources reviewed October 28, 2026.

How does a platform discover capabilities?

A merchant publishes a machine-readable profile describing services, capabilities and payment handling. The platform declares its capabilities too; available session features are determined by what both support. See UCP core concepts.

flowchart LR A[Merchant publishes capabilities] --> C[Negotiate capabilities] B[Platform declares capabilities] --> C C --> D[Use mutually supported checkout and extensions] D --> E[User confirmation or supported authorization] E --> F[Payment, order and subsequent status]

Capabilities can include checkout and extensions, with support varying by version and use case. A UCP profile does not mean every agent can purchase every product.

From selection to order

The platform discovers the merchant profile, interfaces and payment handlers.
The agent submits items and the merchant creates a checkout session.
The user changes shipping or items, and the merchant recalculates price and conditions.
The parties prepare credentials for the available payment method.
Checkout completes and an order is created after required confirmation or authorization.
Order status is synchronized as implemented.

The current checkout specification says users complete checkout manually through a trusted interface unless the AP2 Mandates extension is supported. UCP alone does not imply unattended purchasing.

Participants and payment handlers

Term	Meaning	Example
Payment credential provider	A participant in a transaction	A service providing or processing a credential
Payment handler	A specification for handling a payment instrument	Describes how a platform obtains and submits a compatible credential
Merchant	The business selling and managing an order	Processes order and payment under its configuration

The flow includes negotiating a handler, obtaining a credential and completing submission. Available credentials vary by handler, region and merchant. A protocol name cannot guarantee that a method is available. See the UCP overview.

How does UCP work with AP2?

UCP covers broader commerce interaction: available capabilities, checkout contents and orders. AP2 emphasizes verifiable purchase and payment authorization. The UCP AP2 extension describes a combination in which a merchant signs checkout state, a platform creates a mandate after user consent, and merchant and processor verify according to their roles.

This documented combination still requires compatible versions, extensions and trust. Discovering an endpoint does not establish merchant or product trust; platforms must assess accuracy, terms, refunds and permissions.

Further reading: core concepts, checkout and UCP with AP2.