Glossary
Universal Commerce Protocol (UCP)
The Universal Commerce Protocol (UCP) is the Google- and Shopify-led specification for the full agent commerce lifecycle — discovery, checkout, payment, and post-purchase. Merchants declare what they support at /.well-known/ucp, and it powers Google AI Mode and Gemini shopping (Microsoft Copilot aligns to it).
UCP is transport-agnostic — it works over REST, MCP, and A2A — and uses capability negotiation, so a merchant implements only what it supports and agents degrade gracefully. The spec launched January 11, 2026 and added multi-item carts and real-time catalog queries on March 19, 2026.
Google charges no additional merchant fee for UCP checkout in AI Mode, a notable contrast with ACP's take rate. Our audit pins to a specific UCP version on every run.