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.

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

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.