Universal Commerce Protocol (UCP)
The Universal Commerce Protocol (UCP) is Google's open standard for letting AI agents discover what a shop sells, build a cart and check out on a shopper's behalf. Merchants publish a JSON manifest at /.well-known/ucp that tells agents which capabilities and endpoints they support.
  • UCP was published by Google on 11 January 2026, co-developed with Shopify, Etsy, Wayfair, Target and Walmart.
  • Discovery starts with one file: a JSON manifest at /.well-known/ucp on your own domain.
  • The manifest lists capabilities (checkout, catalogue, cart, identity linking), extensions, payment handlers, endpoints and signing keys.
  • UCP can run over REST, MCP or Google's A2A protocol, and works alongside AP2 for payment authorisation.
  • UCP-powered Buy buttons in AI Mode and Gemini are limited to approved merchants, so clean product data still does most of the work.

The Universal Commerce Protocol (UCP) is an open specification that standardises how an AI agent shops with a business. Instead of every assistant building a custom integration with every retailer, a merchant describes what it supports once, in a standard format, and any compatible agent can use it. Google published UCP on 11 January 2026, developed with Shopify, Etsy, Wayfair, Target and Walmart, with more than 20 other companies endorsing it. The spec lives at ucp.dev and is developed in the open on GitHub.

Why it matters

Agentic commerce turns "find me a waterproof jacket under £150 and buy it" into a transaction completed inside the assistant. If agents cannot read your catalogue or complete your checkout, they will recommend a shop they can. UCP is Google's route for that in AI Mode and Gemini.

The file: /.well-known/ucp

UCP borrows the same idea as robots.txt and sitemap.xml: a well-known file at a predictable address. A merchant publishes a JSON profile at:

 https://www.example.com/.well-known/ucp

An agent fetches it first to learn what the store can do. It typically declares:

  • Version: UCP uses date-based versions, such as 2026-01-11 and 2026-04-08.
  • Services and endpoints: where the API lives, with schema references.
  • Capabilities: named in a reverse-domain style, such as dev.ucp.shopping.checkout and dev.ucp.shopping.catalog.
  • Extensions: optional extras such as discounts, fulfilment options and loyalty.
  • Payment handlers: which payment methods the agent can use.
  • Signing keys: so requests and responses can be verified.

A heavily simplified sketch (check ucp.dev for the exact schema before building):

 {
  "ucp": {
    "version": "2026-04-08",
    "capabilities": ["dev.ucp.shopping.catalog", "dev.ucp.shopping.checkout"],
    "services": { "rest": { "endpoint": "https://www.example.com/ucp" } }
  }
}

How a UCP purchase works

  • The agent reads /.well-known/ucp and negotiates the capabilities both sides support.
  • It searches or looks up products through the catalogue capability.
  • It creates and updates a cart or checkout session with address and delivery choices.
  • Payment runs through a declared handler. In Google's surfaces that is Google Pay, and UCP is compatible with the Agent Payments Protocol (AP2) for signed proof of what the shopper agreed to.
  • Order updates flow back to the agent. The merchant stays the seller of record.

Who can use it today

The spec is public, but Google's native UCP checkout is limited to select merchants who apply through a Merchant Center interest form, for products eligible in the United States, Canada and Australia. Shopify merchants can switch it on from the admin, and payment providers such as PayPal (Braintree) and Stripe offer UCP support so merchants do not build it from scratch.

Common mistakes

  • An invalid manifest. Agents reject files that fail schema validation, and missing the top-level ucp object is a frequent cause.
  • Serving the file through a redirect, behind bot protection or with the wrong Content-Type.
  • Blocking agents at the CDN while the manifest says you welcome them.
  • Prices or stock in the API that disagree with the product page and feed.
  • Losing /.well-known/ files during a platform migration.

How to test

  • Fetch the file with curl -I and confirm a direct 200 and application/json.
  • Validate it against the official schema or a UCP checker.
  • Check logs and CDN events for agents requesting /.well-known/ucp.

The GEO angle

UCP moves GEO from "get cited" to "get bought". Agents still choose products from feeds, structured data and reviews, so Merchant Center data and Product schema remain the foundation. UCP decides whether the agent can finish the job with you.

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