What Is UCP? The Universal Commerce Protocol Explained for eCommerce Merchants
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TL;DR
- What it is: UCP (Universal Commerce Protocol) is an open standard that lets AI agents search a store's catalog, build a cart and complete checkout on a shopper's behalf.
- Who is behind it: Google announced it on 11 January 2026. Shopify, Etsy, Wayfair, Target and Walmart co-developed it, and more than 20 companies including Visa, Mastercard, Stripe and Adyen endorsed it.
- What stays with you: the merchant remains the merchant of record and keeps customer data and the post-purchase relationship.
- What to check first: product data, checkout endpoint and payment provider support.
Until recently, an AI assistant could recommend a product and send the shopper to a product page. UCP defines how the agent goes further. It reads what a store sells, adds items to a cart and starts a checkout, using one shared set of rules.
Why UCP exists
Without a standard, every AI surface needs its own integration with every store. A retailer would build one connection per assistant, and each assistant would build one per retailer.
UCP replaces those one-off connections with a single protocol. A store implements it once, and any agent that speaks UCP can work with it.
In short: one protocol for the whole shopping journey, from discovery to post-purchase support.
What UCP standardizes
UCP covers five capabilities:
- Catalog: agents search and look up products, including variants, inventory and pricing.
- Cart: agents add several items from a single store at once.
- Checkout: one session type that handles pricing, tax and fulfillment logic.
- Identity linking: shoppers receive loyalty or member benefits through OAuth 2.0, without sharing credentials with the agent.
- Orders: webhooks deliver status, tracking and return updates.
Google's March 2026 update made Cart, Catalog and Identity linking available as optional capabilities. Adopters choose which ones to support.
How an agent buys from your store
- Discovery. The agent reads the merchant's UCP profile, published at /.well-known/ucp, to learn which capabilities the store supports.
- Catalog lookup. The agent searches products and pulls live variant, stock and price data.
- Cart. The agent adds the selected items.
- Checkout. The agent opens a checkout session on the merchant's endpoint. Payment runs through a payment handler. AP2 (Agent Payments Protocol) works as the payment layer inside UCP and uses cryptographic proof of the shopper's authorization.
- Order updates. Webhooks keep the agent informed about status, tracking and returns.
Shopper to agent: "Find a waterproof jacket in medium and order it with my saved address."What happens next: the agent searches catalogs, picks a variant that is in stock, builds the cart and starts checkout with that merchant.
What stays under your control
You remain the merchant of record. Customer data and the relationship after the sale stay with you.
- You decide which capabilities to support.
- Payments run through your own payment service provider, which must be able to process Google's tokens.
- Your platform can host the profile for you. Google's documentation describes the platform generating and hosting the /.well-known/ucp JSON profile and configuring the checkout endpoints on the merchant domain.
Shopify merchants manage product data centrally from Shopify Admin through Agentic Storefronts. Shopify lists ChatGPT, Microsoft Copilot, Google AI Mode and the Gemini app as channels merchants can sell in.
What merchants need in place
Google lists these requirements for adopting UCP:
- Merchant Center account: complete product feeds, brand assets, return policies and business contact information.
- Checkout endpoint: native checkout is the default path. Embedded checkout through an iframe is optional for complex checkout flows.
- Payment handler: your PSP must process Google's tokens.
- UCP profile: a /.well-known/ucp file that tells agents what you support.
UCP and ACP
ACP (Agentic Commerce Protocol) was developed by OpenAI and Stripe and announced on 29 September 2025. Both protocols aim at the same outcome: an agent that completes a purchase in a store. They differ in who hosts what and which AI surfaces they serve. We compare them in a separate article.
FAQ
Is UCP only for Shopify stores?
No. UCP is an open standard with many co-developers and native SDKs for several programming languages. Shopify implements it through Agentic Storefronts, and other platforms and custom stores can implement the protocol too.
Does UCP replace my checkout?
No. UCP exposes your existing checkout to agents through a defined endpoint. You stay the merchant of record.
Do I pay a fee to use UCP?
Google's FAQ does not disclose fees. Confirm costs with your platform and payment provider.
Conclusions
Which AI surfaces use UCP today?
Google's documentation names AI Mode in Google Search and the Gemini app. Rollout is staged, so check Google's current documentation for availability.