What is Google's UCP (Universal Commerce Protocol)?

UCP is the Universal Commerce Protocol, the standard Google wants AI agents to use to buy from stores without a separate integration for each one. Google introduced it on January 11, 2026, and it is the piece behind the buy button in Google AI Mode and in Gemini.⁠^{[1]Google, official blog. New tech and tools for retailers to succeed in an agentic shopping era} It matters to a store for two reasons: it defines what the store has to publish so an AI agent can buy from it, and its timeline says when each piece reaches each country. Its counterpart in ChatGPT is ACP (Agentic Commerce Protocol).

How it works

Google describes it as an open standard for agentic commerce that covers the whole purchase journey, developed with Shopify, Etsy, Wayfair, Target and Walmart, endorsed by more than twenty companies, including Adyen, American Express, Mastercard, Stripe and Visa, and compatible with A2A (agent-to-agent), AP2 (Agent Payments Protocol) and MCP (Model Context Protocol).⁠^{[1]Google, official blog. New tech and tools for retailers to succeed in an agentic shopping era} Today the protocol's website lists Amazon, Microsoft, Meta, Salesforce and Stripe, among others, as co-developers, plus more than sixty endorsing organizations.⁠^{[2]Universal Commerce Protocol. Universal Commerce Protocol}

The central mechanism is discovery. Each store publishes a profile at /.well-known/ucp with the services, capabilities and payment methods it supports, and the agent sends the address of its own profile with every request so both sides can negotiate what they can do together.⁠^{[3]Universal Commerce Protocol. UCP Specification Overview (version 2026-08-25)} Google explains it as a standard JSON manifest that lets the agent discover features, endpoints and payment configurations without hand-written integrations.⁠^{[4]Google Developers Blog. Under the Hood: Universal Commerce Protocol (UCP)}

The specification splits four roles: the business, which publishes its capabilities and serves requests; the platform, which is the agent or app doing the buying; the credential provider for payments; and the payment service provider. Each capability has a domain-style name, such as dev.ucp.shopping.checkout, and extensions add optional features to a capability. The transports are REST, MCP, A2A and a protocol for embedded experiences.⁠^{[3]Universal Commerce Protocol. UCP Specification Overview (version 2026-08-25)} The published shopping capabilities are catalog, cart, checkout, identity linking with OAuth 2.0 and order; there is a draft for lodging and food delivery is announced.⁠^{[2]Universal Commerce Protocol. Universal Commerce Protocol} The current version of the specification is the one dated August 25, 2026.⁠^{[3]Universal Commerce Protocol. UCP Specification Overview (version 2026-08-25)}

What works today and what is announced

To get in, Google asks you to prepare your Google Merchant Center account (shipping, returns and feed), join the waitlist, set up Google Pay as a payment method and publish the UCP profile; Google has to approve the integration before it appears in AI Mode or Gemini.⁠^{[7]Google for Developers. UCP on Google: integration guide overview}

Shopify already works on UCP: agents authenticate, search its catalog, build carts and track orders using this protocol. The agent turns the cart into a checkout and sends the buyer to the store to pay; trusted agents can complete it directly.⁠^{[8]Shopify, developer documentation. Build commerce agents with UCP}

In a store

Here is what the profile of a fictional example store would look like at https://coffee-makers-example.com/.well-known/ucp, with the structure of the specification's own example: one shopping service over REST and the checkout capability.⁠^{[3]Universal Commerce Protocol. UCP Specification Overview (version 2026-08-25)} The signing keys, which a real profile includes, are left out here.

{
  "ucp": {
    "version": "2026-08-25",
    "services": {
      "dev.ucp.shopping": [
        {
          "version": "2026-08-25",
          "spec": "https://ucp.dev/2026-08-25/specification/overview/",
          "transport": "rest",
          "endpoint": "https://coffee-makers-example.com/ucp/v1",
          "schema": "https://ucp.dev/2026-08-25/services/shopping/rest.openapi.json"
        }
      ]
    },
    "capabilities": {
      "dev.ucp.shopping.checkout": [
        {
          "version": "2026-08-25",
          "spec": "https://ucp.dev/2026-08-25/specification/shopping/checkout",
          "schema": "https://ucp.dev/2026-08-25/schemas/shopping/checkout.json"
        }
      ]
    },
    "payment_handlers": {}
  }
}

What that file says is short: the store speaks UCP in its August 2026 version, serves requests over REST at a specific address and knows how to process a payment. An agent that reads it knows what it can ask for; one that does not find it has no way to know the store accepts agents.

How to check

1. Open https://your-domain/.well-known/ucp in the browser. If it exists, look at the version, services and capabilities it declares.⁠^{[3]Universal Commerce Protocol. UCP Specification Overview (version 2026-08-25)}
2. Review Merchant Center: feed without errors, shipping and returns configured. It is Google's first requirement.⁠^{[7]Google for Developers. UCP on Google: integration guide overview}
3. If you sell in the United States, complete the technical implementation and the interest form; Google lets you know when it selects you, and then onboarding opens in Merchant Center.⁠^{[6]Google Merchant Center Help. How to onboard to the Universal Commerce Protocol in Merchant Center}
4. If you sell on Shopify, check which UCP capabilities your platform already offers before building anything custom.⁠^{[8]Shopify, developer documentation. Build commerce agents with UCP}

Related concept: ACP

ACP (Agentic Commerce Protocol) is OpenAI and Stripe's protocol for the same job: letting an agent discover and buy from a store. They are alike in the essentials, because both leave the merchant as the seller and both can use MCP as a transport.⁠^{[9]OpenAI and Stripe. Agentic Commerce Protocol}⁠^{[3]Universal Commerce Protocol. UCP Specification Overview (version 2026-08-25)} They differ in who drives them and where they are used: UCP comes from Google with Shopify and large retail chains, and it is the one behind AI Mode and Gemini;⁠^{[1]Google, official blog. New tech and tools for retailers to succeed in an agentic shopping era} ACP is the one that powers ChatGPT. What sets UCP apart in its design is the public profile at /.well-known/ucp and the negotiation of capabilities on every request.⁠^{[3]Universal Commerce Protocol. UCP Specification Overview (version 2026-08-25)}

To go further, agentic commerce separates discovering, recommending and buying, and the agentic commerce reading path puts the rest of the protocols in order.