UCP solves the N-to-N integration problem in commerce by providing a single open standard that enables AI platforms, businesses, and payment providers to interoperate without custom integrations. Built on REST, JSON-RPC, MCP, and A2A protocols, UCP standardizes checkout, order management, and payment processing APIs.

The protocol uses a capability-based architecture where businesses publish their supported features at `/.well-known/ucp`, and platforms negotiate capabilities automatically during request/response flows. Core capabilities include checkout sessions (`dev.ucp.shopping.checkout`), order lifecycle management (`dev.ucp.shopping.order`), and OAuth 2.0-based identity linking.

Co-developed by Google, Shopify, Etsy, Wayfair, Target, and Walmart, with support from 60+ organizations including Stripe, PayPal, and Visa. Transport-agnostic design supports REST APIs, MCP for LLM integration, and A2A for agent-to-agent communication.

The article covers architecture, core capabilities, extensions, payment architecture, and integration patterns. Includes code examples and implementation details.

Nice to see an open standard for this instead of proprietary integrations.

Made a validator at ucptools.dev to help with implementation - checks the full spec compliance and tells you exactly what to fix.

The /.well-known/ucp pattern is smart - same discovery mechanism as security.txt, apple-app-site-association, etc.

Official post: https://blog.google/products/ads-commerce/agentic-commerce-a... (https://news.ycombinator.com/item?id=46581509)