Universal Commerce Protocol (UCP)
How do AI agents shop?
UCP is Google's open standard for agent-to-merchant commerce. Where A2A handles agent communication, UCP handles the buying — checkout, discounts, fulfillment, returns. One protocol so any agent can transact with any merchant.
Discovery
Merchants publish capabilities at /.well-known/ucp — the same pattern as A2A's agent cards. An agent hits this endpoint and learns what commerce operations the merchant supports.
| Field | Purpose | Example |
|---|---|---|
services | Available commerce operations | Checkout, Discount, Fulfillment |
capabilities | What each service supports | Cart management, coupon validation, shipment tracking |
transport | How to connect | REST, A2A binding, MCP binding |
authentication | Required auth | OAuth2, API key |
Discovery is the onramp. No integration guides, no partner agreements. Hit the endpoint, read the schema, transact.
Services
UCP defines three core service interfaces:
| Service | What It Does | Operations |
|---|---|---|
| Checkout | Cart to payment to order | Create cart, add items, apply payment, confirm order |
| Discount | Pricing intelligence | Query available discounts, validate coupons, apply promotions |
| Fulfillment | Post-purchase logistics | Track shipment, manage returns, confirm delivery |
Each service is optional. A merchant implements what they support. An agent inspects capabilities before attempting operations — no trial-and-error.
Commerce Journey
The full loop from intent to delivery:
BROWSE → CART → DISCOUNT → CHECKOUT → PAYMENT → FULFILLMENT → FEEDBACK
↓ ↓ ↓ ↓ ↓ ↓ ↓
Agent Agent Agent Agent AP2/x402 Merchant Agent
finds builds applies confirms authorizes ships evaluates
items basket coupons order payment product experience
| Stage | Protocol | Who Acts |
|---|---|---|
| Browse + Cart | UCP Checkout | Agent queries merchant catalog, builds cart |
| Discount | UCP Discount | Agent finds and applies best available pricing |
| Payment | AP2 | Agent authorizes payment via VDC mandate |
| Settlement | Card rails, stablecoins, or x402 | Payment service provider settles |
| Fulfillment | UCP Fulfillment | Merchant ships, agent tracks |
Transport Bindings
UCP is transport-flexible. Three official bindings:
| Binding | How It Works | Best For |
|---|---|---|
| REST | Standard HTTP endpoints | Direct merchant integrations |
| A2A | Commerce operations wrapped as A2A tasks | Agent-to-agent commerce delegation |
| MCP | Commerce operations exposed as MCP tools | AI assistants shopping on behalf of users |
The A2A binding means any agent that speaks A2A can also shop via UCP. The MCP binding means any LLM with MCP tool access can transact. Same operations, three entry points.
Merchant of Record
UCP preserves the merchant-of-record model. The merchant owns the transaction:
| Responsibility | Who Owns It |
|---|---|
| Product catalog | Merchant |
| Pricing | Merchant |
| Tax calculation | Merchant |
| Order fulfillment | Merchant |
| Customer service | Merchant |
| Payment processing | Merchant's PSP |
The agent is a buyer, not an intermediary. This matters for regulation — the merchant retains liability, compliance obligations, and customer relationship. The protocol standardizes the interface, not the business.
Partners
20+ launch partners across the commerce stack:
| Layer | Partners |
|---|---|
| Marketplaces | Shopify, Etsy, Wayfair, Target, Walmart |
| Payment | Visa, Mastercard, Stripe, Adyen, American Express |
| Commerce platforms | BigCommerce, WooCommerce |
Shopify is building UCP natively. When Shopify's 4M+ merchants gain UCP endpoints, any A2A-capable agent can buy from any Shopify store without custom integration.
Where UCP Sits
A2A (communication) → UCP (commerce) → AP2 (payment) → Settlement
| Protocol | What It Does | Analogy |
|---|---|---|
| A2A | Agents find and talk to each other | DNS + TCP |
| UCP | Agents buy and sell | HTTP (the commerce API) |
| AP2 | Agents authorize payments | Credit card authorization |
| Settlement | Value actually moves | Bank clearing |
UCP is the commerce API for the agentic economy. A2A provides the transport. AP2 provides the payment authorization. Together they form Google's agent commerce stack.
Context
- Agent Protocols — The protocol landscape
- A2A Protocol — Communication layer UCP rides on
- AP2 — Payment authorization for UCP transactions
- Agent Commerce — The standards war: UCP vs ACP
- Smart Contracts — On-chain settlement infrastructure
- Payment Rails — Traditional and crypto settlement layers
Links
- UCP Documentation — Google's official documentation
- Google Agentic Commerce — Vision for agent-powered shopping
Questions
When every merchant publishes a /.well-known/ucp endpoint, does the agent that shops best become the ultimate consumer?
- If UCP standardizes the buy side, what happens to the differentiation merchants built through custom checkout experiences?
- Does the merchant-of-record model survive when the buyer is an algorithm that optimizes purely for price?
- At what transaction volume do agents need their own discount negotiation — and does UCP support that?