UCP — Universal Commerce Protocol

“The common language for platforms, agents and businesses.”

What Is UCP

UCP (Universal Commerce Protocol) is an open protocol co-developed by six industry leaders: Google, Shopify, Etsy, Wayfair, Target, and Walmart. It defines a standardized interaction language between AI agents and merchants, covering the complete commerce lifecycle — product discovery, checkout management, identity linking, order tracking, and payment token exchange. Official Specification: ucp.dev | GitHub: Universal-Commerce-Protocol/ucp (2.6k stars) | License: Apache 2.0 Latest Spec Version: 2026-04-08 (date-based versioning strategy)

Ecosystem

UCP boasts 30+ ecosystem partners spanning payments, finance, and retail:

Sector	Partners
Payment Processing	Adyen, Block (Square), PayPal, Stripe
Buy Now Pay Later	Affirm, Klarna
Card Networks / Finance	American Express, Visa, Ant International
Retailers	Best Buy, Target, Walmart
E-Commerce Platforms	Shopify, Etsy, Wayfair

Design Principles

Principle	Meaning
Merchant-Centric	Merchants retain full control over business rules and always serve as the Merchant of Record
Interface-Agnostic	Supports chat, visual, voice, and other interaction modalities
Open Interoperability	Compatible with OAuth 2.0, AP2 payment protocol, A2A agent-to-agent communication, MCP tool protocol, and other existing standards
Namespace Governance	Reverse-domain naming (`dev.ucp.` managed by UCP official; `com.vendor.` managed by vendors)

Four Core Capabilities

UCP defines four core capabilities, each identified by a reverse-domain namespace:

1. Checkout

Namespace: dev.ucp.shopping.checkout AI agents can create checkout sessions and manage shopping carts, shipping methods, and payment information. A checkout session has 6 standard states (incomplete, requires_escalation, ready_for_complete, complete_in_progress, completed, canceled) and supports 5 operations (Create/Get/Update/Complete/Cancel). All monetary amounts use ISO 4217 minor units.

2. Identity Linking

Namespace: dev.ucp.common.identity_linking Built on the OAuth 2.0 Authorization Code flow, with authorization server discovery via /.well-known/oauth-authorization-server. Supports token revocation (RFC 7009).

3. Order Management

Namespace: dev.ucp.shopping.order Tracks line item status (processing/partial/fulfilled/removed) and fulfillment events (processing/shipped/in_transit/delivered, etc.). Supports adjustments such as refunds, returns, and credits. Webhooks use RFC 9421 signatures for security.

4. Payment Token Exchange

Namespace: dev.ucp.shopping.payment_token_exchange A three-step lifecycle: Negotiation, Acquisition, and Completion. Payment processors use reverse-DNS naming, and credential flow is unidirectional: from platform to merchant.

Transport Mechanisms

UCP supports four transport mechanisms to accommodate different integration scenarios:

Transport	Schema Format	Use Case
REST	OpenAPI 3.x	Server-to-server integration
MCP	OpenRPC (JSON-RPC 2.0)	AI tool connections (provides `search_catalog`, `lookup_catalog`, `get_product` tools)
A2A	Agent Card Specification	Inter-agent collaboration
Embedded	OpenRPC schema	Embedded UI scenarios

UCP and Other Protocols

Protocol	Purpose	Relationship with UCP
ACP (OpenAI/Stripe)	AI agent ordering and payments	UCP covers broader scope (discovery + checkout + orders + payment tokens); ACP focuses on the ChatGPT ecosystem
MCP (Anthropic)	AI connections to external tools	UCP can expose commerce capabilities through MCP transport (OpenRPC schema)
OAuth 2.0	Identity authentication	UCP uses OAuth 2.0 Authorization Code as its identity linking standard
A2A (Google)	Agent-to-agent communication	UCP implements multi-agent collaboration through A2A transport
RFC 9421	HTTP message signatures	UCP uses this standard for webhooks and authentication

Who Should Pay Attention to UCP

Role	Why It Matters
Shopify Merchants	Shopify is a UCP co-developer and is expected to offer native support
Platform Developers	Adopting UCP enables your platform to interface with all UCP-compatible AI agents
AI Application Developers	Implementing a UCP client lets you connect to all UCP merchants; MCP transport provides direct integration
Payment Service Providers	The Payment Token Exchange capability defines a standardized agent payment flow
Independent Merchants	Deploying a `/.well-known/ucp` Profile is all it takes for AI agents to discover your capabilities

Chapter Index

Core Concepts — Protocol architecture, namespaces, capability negotiation algorithm, UCP Profile
Checkout API — 6 states, 5 operations, embedded UI, ISO 4217 amount handling
Identity Linking — OAuth 2.0 Authorization Code, token revocation, scope management
Order Management — Line item status, fulfillment events, adjustments, webhook signatures
Product Data and Transport — MCP tools, REST/A2A/Embedded transports, data formats
Security and Authentication — RFC 9421 signatures, JWK keys, mTLS, Content-Digest
Merchant Integration Guide — /.well-known/ucp Profile deployment, capability declarations
Platform Integration Guide — Capability negotiation algorithm, extension mechanisms, multi-platform strategies
Testing and Validation — Profile validation, checkout flow testing, security compliance checks
Case Studies and Extensions — Buyer Consent, AP2 Mandate extensions, integration paths

AI Prompt: UCP Integration Planning

If you want an AI assistant to help plan your UCP integration:

Help me understand and plan UCP (Universal Commerce Protocol) integration.

Preparation:
1. Please read the UCP official documentation: https://ucp.dev
2. Review the UCP GitHub repository: Universal-Commerce-Protocol/ucp

My situation:
- Platform: [Shopify/WooCommerce/Custom-built]
- Tech stack: [Your tech stack]
- Product count: [Number]
- Required capabilities: [Product discovery/Checkout/Identity linking/Order management/Payment tokens]

Please provide:
1. A plain-language summary of UCP core concepts
2. A configuration plan for the /.well-known/ucp Profile
3. A list of capability endpoints to implement
4. A phased integration plan
5. Security requirements (signing keys, authentication methods)
6. Estimated level of effort

UCP is a rapidly evolving protocol. The latest spec version is 2026-04-08. This book is based on that version of the official documentation. Always refer to the latest version at ucp.dev. GitHub repository: Universal-Commerce-Protocol/ucp

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