Universal Commerce Protocol (UCP)
UCP describes how a store tells agents what it supports and how agents search a catalog, build a cart and hand off to checkout. A store publishes a profile at /.well-known/ucp and can expose MCP tools such as search_catalog and create_cart. Google uses UCP for agent checkout in AI Mode and Gemini.
Governed by: Open standard launched by Google with commerce partners including Shopify. Published openly at ucp.dev.
Official source: ucp.dev specification · Google Merchant Center UCP guide
What ARC sees
Live: n = 11,824 stores with a completed HTTP check, latest as of 23 Oct 2026 (UTC). Live figures (n = 11,824) update hourly from saved checks. Downloads are the dated weekly snapshot 2026-10-12.r3, n = 3,318, so their counts can differ.
Declared
8673 / 1182473.4%
Measured/.well-known/ucp answered HTTP 200 with a body
Valid
8566 / 1182472.4%
MeasuredProfile passed ARC's validation
Usable
7937 / 1182467.1%
MeasuredThe UCP catalog tool returned the tested product
Transacts
7498 / 1182463.4%
MeasuredUCP create_cart returned a checkout link
What ARC checks
- Fetches /.well-known/ucp and validates the profile. That GET does not follow redirects. Any 3xx is not a valid profile. ARC tries the host given, then the other of apex and www when the first response is not a valid profile and is not a stop.
- Lists tools on the store's UCP MCP endpoint. Those POST requests stay on the first response.
- Calls the catalog tool for one real product.
- Calls create_cart for that product and records whether a checkout link came back. The cart is cancelled when the store offers cancel_cart. No order is placed.
What ARC can't check from outside
- Whether checkout completes or payment succeeds.
- Merchant Center feed flags and Google approval.
Methodology
Counts use each store's latest completed HTTP check saved by ARC. Failed checks are left out of the denominator. Each host counts once.
Measured means ARC observed it directly. Inferred means ARC links two observations that do not prove each other. Not measured means ARC has no saved evidence, and the count is not zero adoption.
A checkout link means a cart was created for one real product. It is not a completed purchase. ARC never places orders.
The sample is ARC's curated store list plus stores people checked. It is not all of e-commerce. Treat percentages as rates in this sample.
Reads make no store requests and no model calls.
Cite this
ARC Protocol Matrix: UCP, arcreport.ai/protocols/ucp, accessed 2026-10-23. Licensed CC-BY-4.0. Data: arcreport.ai/data.