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UCP — Universal Commerce Protocol

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

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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)

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Ecosystem

UCP boasts 30+ ecosystem partners spanning payments, finance, and retail:
SectorPartners
Payment ProcessingAdyen, Block (Square), PayPal, Stripe
Buy Now Pay LaterAffirm, Klarna
Card Networks / FinanceAmerican Express, Visa, Ant International
RetailersBest Buy, Target, Walmart
E-Commerce PlatformsShopify, Etsy, Wayfair

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Design Principles

PrincipleMeaning
Merchant-CentricMerchants retain full control over business rules and always serve as the Merchant of Record
Interface-AgnosticSupports chat, visual, voice, and other interaction modalities
Open InteroperabilityCompatible with OAuth 2.0, AP2 payment protocol, A2A agent-to-agent communication, MCP tool protocol, and other existing standards
Namespace GovernanceReverse-domain naming (dev.ucp.* managed by UCP official; com.vendor.* managed by vendors)

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Four Core Capabilities

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

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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.

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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).

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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.

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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.

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Transport Mechanisms

UCP supports four transport mechanisms to accommodate different integration scenarios:
TransportSchema FormatUse Case
RESTOpenAPI 3.xServer-to-server integration
MCPOpenRPC (JSON-RPC 2.0)AI tool connections (provides search_catalog, lookup_catalog, get_product tools)
A2AAgent Card SpecificationInter-agent collaboration
EmbeddedOpenRPC schemaEmbedded UI scenarios

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UCP and Other Protocols

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

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Who Should Pay Attention to UCP

RoleWhy It Matters
Shopify MerchantsShopify is a UCP co-developer and is expected to offer native support
Platform DevelopersAdopting UCP enables your platform to interface with all UCP-compatible AI agents
AI Application DevelopersImplementing a UCP client lets you connect to all UCP merchants; MCP transport provides direct integration
Payment Service ProvidersThe Payment Token Exchange capability defines a standardized agent payment flow
Independent MerchantsDeploying a /.well-known/ucp Profile is all it takes for AI agents to discover your capabilities

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Chapter Index

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

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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