UCP — Universal Commerce Protocol

What is UCP?

UCP (Universal Commerce Protocol) is an open commerce transaction standard for AI agents from Google, developed in collaboration with Shopify, Etsy, Wayfair, Target, Walmart, and 20+ endorsers (including Visa, Mastercard, and Stripe). It covers the full journey: discovery → cart → checkout → order management.

Why do you need UCP?

When an AI agent receives a task like “order delivery,” it needs a standard way to complete the entire commercial scenario autonomously. UCP is broader than x402 or MPP (which handle only payment) — it standardizes the full cycle:

Stage	What the agent does
Discovery	Finds the product/service through a catalog
Cart	Builds the cart, checks availability
Checkout	Places the order and payment
Order management	Tracks status, handles returns

The protocol supports REST and JSON-RPC transports and works with agent stacks AP2/A2A/MCP. It powers checkout in Google AI Mode and Gemini. Endorsers include Shopify, Etsy, Walmart, Visa, Mastercard, and Stripe.

How do you implement UCP?

Declare UCP support in ai-agent.json:

{
  "payments": {
    "ucp": "https://api.example.com/ucp"
  }
}

Or via a Link header:

Link: <https://api.example.com/ucp>; rel="ucp-endpoint"

Full integration involves implementing UCP endpoints for each stage (discovery, cart, checkout, order). Documentation: developers.google.com/merchant/ucp.

How do we check UCP?

The UCP check in the scanner is informational (does not affect the main score). The scanner checks for protocol declaration in two ways:

1. GET /.well-known/ai-agent.json → payments.ucp field
2. HEAD / → Link header with rel="ucp-endpoint"

The actual commercial flow is not tested. If a declaration is found → pass, if absent → fail.