In short. Universal Commerce Protocol connects commerce participants through shared capability definitions, profiles and version negotiation.

Definition: Universal Commerce Protocol (UCP) is an open standard for communication between shopping platforms, businesses and payment providers. It defines commerce capabilities, the functions a participant supports, and a way to identify shared functions and versions.

Key facts

Google's UCP announcement, dated 11 January 2026, names Shopify, Etsy, Wayfair, Target and Walmart as co-developers.
As of 17 October 2026, the official specification selects a business protocol profile, a machine-readable description of supported functions, before negotiating compatible capabilities and extensions.
The Checkout Capability requires the user to finalize checkout through a trusted interface unless the Agent Payments Protocol (AP2) Mandates extension is supported.
Google's integration guide identifies the business as the Merchant of Record, the merchant responsible for the transaction.

Which commerce functions does UCP describe?

A capability is a supported function within a service, the interface for a commerce area such as shopping. An extension is an optional module that adds functionality to a capability. The specification overview gives fulfillment as an extension of checkout and discounts as an extension that can apply to checkout and cart capabilities.

The checkout specification defines a session whose status tells the platform what happens next. For example, requires_escalation directs the platform to hand the buyer over through continue_url when buyer input is needed. Fulfillment details are optional, allowing checkout for digital goods without the delivery details relevant to physical products.

The Identity Linking Capability uses OAuth 2.0, an authorization protocol, to obtain permission to act for a user on a business's site. This supports access to saved addresses, loyalty benefits and order history. Public and agent-authenticated operations can also operate without account linking.

The Order Capability represents the current state of an order. It separates delivery expectations from shipment events and records post-order adjustments such as refunds or returns. The same order schema serves retrieval requests and event notifications.

How does interoperability work?

The official overview separates commerce functions from the transport used to communicate them. Its service definitions include REST, an HTTP API approach; Model Context Protocol (MCP), a tool communication protocol; Agent2Agent (A2A), a protocol for communication between agents; and an embedded protocol for integrated interfaces.

Participants advertise versions and capabilities in machine-readable profiles. The platform first selects a supported business profile. Capability negotiation then selects shared functions using exact version matches. Extensions identify the capabilities they augment through the extends field. Interoperability therefore depends on the versions, functions and transport bindings the participants actually implement.

Agent Payments Protocol (AP2) provides an optional authorization layer through the AP2 Mandates extension. When negotiated, it adds signed checkout terms and mandates proving user authorization. It is a separate choice within the UCP capability framework.

What does a website operator implement?

The profile specification places the business's machine-readable profile at this path:

/.well-known/ucp

The profile identifies services, capabilities and payment handlers, which describe how payment instruments are processed. A website operator checks the advertised versions, service endpoints and capability schemas against the integration being built.

Google's UCP guide describes a Google-specific implementation using Merchant Center shopping feeds. It offers native checkout and an optional embedded checkout path for specific approved merchants with bespoke or complex flows. The guide directs merchants to a waitlist for participation. These integration conditions sit alongside the open protocol's technical requirements.

FAQ

Does UCP require an entirely autonomous purchase?

The checkout specification requires you to finalize the purchase through a trusted interface unless the AP2 Mandates extension is supported. It also defines a handoff URL for checkout states that require buyer input.

Can a business choose its supported functions?

Yes. The official overview uses profiles to advertise capabilities and extensions, then negotiates their shared versions. Your integration's active functions depend on that negotiated set.

How does a merchant approach Google's implementation?

Google's integration guide points you to its documentation and participation waitlist. It describes Merchant Center feeds and the native and embedded checkout options.

Sources

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