Universal Commerce Protocol (UCP): The Complete 2026 Guide to Agentic Commerce Standards

🎯 Core Takeaways (TL;DR)

• Universal Commerce Protocol (UCP) is an open standard enabling seamless interoperability between AI platforms, businesses, payment providers, and credential providers without custom integrations
• The Universal Commerce Protocol solves fragmented commerce journeys by providing standardized APIs for checkout, order management, identity linking, and payment processing
• Built on industry standards (REST, JSON-RPC, MCP, A2A) with built-in support for AP2 Protocol and A2A Protocol, the Universal Commerce Protocol enables true agentic commerce
• Co-developed by industry leaders including Google, Shopify, Etsy, Wayfair, Target, and Walmart, with endorsement from 60+ organizations including Adyen, Mastercard, PayPal, Stripe, and Visa

Table of Contents

1. What is Universal Commerce Protocol (UCP)?
2. Why Universal Commerce Protocol Matters
3. Universal Commerce Protocol Architecture
4. Core Capabilities of Universal Commerce Protocol
5. Universal Commerce Protocol Extensions
6. Universal Commerce Protocol and Payment Architecture
7. Universal Commerce Protocol Transport Layers
8. Universal Commerce Protocol Integration with AP2 and A2A
9. Getting Started with Universal Commerce Protocol
10. Universal Commerce Protocol Roadmap
11. Common Questions About Universal Commerce Protocol

What is Universal Commerce Protocol (UCP)?

The Universal Commerce Protocol (UCP) is an open standard designed to facilitate communication and interoperability between diverse commerce entities. In a fragmented landscape where consumer surfaces/platforms, businesses, payment providers, and identity providers operate on different systems, the Universal Commerce Protocol provides a standardized common language and functional primitives.

The Universal Commerce Protocol defines building blocks for agentic commerce—from discovering and buying to post-purchase experiences—allowing the ecosystem to interoperate through one standard, without custom builds. The Universal Commerce Protocol serves as the common language for platforms, agents, and businesses, enabling seamless collaboration across the entire commerce lifecycle.

Key Goals of Universal Commerce Protocol

The Universal Commerce Protocol is built around four fundamental objectives:

💡 Professional Insight

The Universal Commerce Protocol is designed to solve the "N-to-N" complexity problem in commerce. Instead of requiring custom integrations between every platform and every business, UCP provides a single standard that all parties can implement, dramatically reducing integration costs and time-to-market.

Why Universal Commerce Protocol Matters

Traditional commerce systems assume humans directly interact with trusted surfaces. The rise of AI agents breaks this fundamental assumption, creating three critical challenges that the Universal Commerce Protocol addresses:

1. Fragmented Commerce Journeys

Without standardization, each platform must build custom integrations for every business, leading to:

• Abandoned carts due to integration failures
• Frustrated shoppers experiencing inconsistent experiences
• High development costs for businesses supporting multiple platforms

The Universal Commerce Protocol eliminates this fragmentation by providing a single standard that works across all platforms and businesses.

2. Agentic Commerce Requirements

AI agents need to:

• Discover business capabilities dynamically
• Negotiate payment methods securely
• Handle complex checkout flows programmatically
• Manage post-purchase experiences

The Universal Commerce Protocol provides the primitives needed for true agentic commerce, enabling AI agents to complete purchases autonomously while maintaining security and user control.

3. Payment Interoperability

The payment ecosystem involves multiple parties:

• Platforms (AI agents, apps, websites)
• Businesses (retailers, service providers)
• Payment Credential Providers (digital wallets, banks)
• Payment Service Providers (Stripe, Adyen, PayPal)

The Universal Commerce Protocol decouples payment instruments from payment handlers, enabling open interoperability between providers while maintaining security and compliance.

Universal Commerce Protocol Architecture

The Universal Commerce Protocol employs a role-based architecture with four primary participants:

Roles & Participants

Core Concepts

The Universal Commerce Protocol revolves around three fundamental constructs:

1. Capabilities

Capabilities are standalone core features that a business supports. These are the "verbs" of the protocol.

Core Capabilities:

• dev.ucp.shopping.checkout - Facilitates checkout session creation and management
• dev.ucp.shopping.order - Enables order lifecycle management and webhooks
• dev.ucp.common.identity_linking - OAuth 2.0-based account linking

2. Extensions

Extensions are optional capabilities that augment another capability via the extends field. Extensions appear in ucp.capabilities[] alongside core capabilities.

Official Extensions:

• dev.ucp.shopping.fulfillment - Extends checkout with shipping/pickup options
• dev.ucp.shopping.discount - Extends checkout with discount code support
• dev.ucp.shopping.buyer_consent - Extends checkout with privacy consent fields
• dev.ucp.shopping.ap2_mandate - Extends checkout with AP2 Protocol cryptographic mandates

3. Services

Services define the lower-level communication layers used to exchange data. The Universal Commerce Protocol is transport-agnostic but defines specific bindings for interoperability.

Supported Transports:

• REST API - Primary transport using OpenAPI 3.x
• MCP (Model Context Protocol) - JSON-RPC binding for LLM integration
• A2A (Agent2Agent Protocol) - Agent Card specification for agent-to-agent communication
• Embedded Protocol - JSON-RPC for embedded checkout experiences

Discovery and Negotiation

The Universal Commerce Protocol uses a server-selects architecture where:

1. Businesses publish their profile at /.well-known/ucp declaring supported capabilities
2. Platforms advertise their profile URI with each request
3. Businesses compute the capability intersection (what both parties support)
4. Extensions without their parent capability are automatically pruned

This negotiation happens automatically within the normal request/response flow, enabling efficient capability discovery without separate negotiation phases.

Core Capabilities of Universal Commerce Protocol

Checkout Capability

The checkout capability (dev.ucp.shopping.checkout) is the foundation of the Universal Commerce Protocol. It enables platforms to facilitate checkout sessions with complex cart logic, dynamic pricing, tax calculations, and payment processing.

Key Features:

• Multi-item cart support
• Dynamic pricing and tax calculation
• Payment handler negotiation
• Error handling with severity levels
• Continue URL for buyer handoff

Checkout Status Lifecycle:

incomplete ↔ requires_escalation
     ↓              ↓
ready_for_complete → complete_in_progress → completed
     ↓
  canceled (can occur from any state)

Status Values:

• incomplete - Missing required information, platform should resolve via Update Checkout
• requires_escalation - Requires buyer input via continue_url
• ready_for_complete - All information collected, platform can finalize
• complete_in_progress - Business processing completion
• completed - Order placed successfully
• canceled - Session invalid or expired

Order Capability

The order capability (dev.ucp.shopping.order) enables businesses to push asynchronous updates about order lifecycle events including shipping, delivery, returns, and refunds.

Key Components:

1. Line Items - What was purchased, with quantity tracking (total, fulfilled)
2. Fulfillment - Delivery expectations and events (shipped, in_transit, delivered)
3. Adjustments - Post-order events (refunds, returns, credits, disputes)

Event Mechanism:
Businesses send order updates via webhooks to platform-provided URLs. Webhooks are signed using JWT (RFC 7797) for verification.

Identity Linking Capability

The identity linking capability (dev.ucp.common.identity_linking) enables platforms to obtain OAuth 2.0 authorization to perform actions on behalf of users.

Key Features:

• Standard OAuth 2.0 Authorization Code flow
• RFC 8414 discovery via /.well-known/oauth-authorization-server
• UCP-specific scopes (e.g., ucp:scopes:checkout_session)
• Token revocation support (RFC 7009)
• Cross-account protection via OpenID RISC Profile 1.0

Universal Commerce Protocol Extensions

Fulfillment Extension

The fulfillment extension (dev.ucp.shopping.fulfillment) adds shipping and pickup options to checkout sessions.

Key Features:

• Multiple fulfillment methods (shipping, pickup, etc.)
• Destination management (addresses, store locations)
• Shipping option groups with pricing
• Available methods for alternative fulfillment options
• Method-agnostic rendering (platforms don't need to understand specific types)

Example Structure:

{
  "fulfillment": {
    "methods": [{
      "type": "shipping",
      "line_item_ids": ["shirt", "pants"],
      "destinations": [...],
      "groups": [{
        "options": [
          {"id": "standard", "title": "Standard Shipping", "totals": [...]},
          {"id": "express", "title": "Express Shipping", "totals": [...]}
        ]
      }]
    }]
  }
}

Discount Extension

The discount extension (dev.ucp.shopping.discount) enables discount code submission and automatic discount application.

Key Features:

• Submit one or more discount codes
• Receive applied discounts with human-readable titles
• Rejected codes communicated via messages[] array
• Automatic discounts surfaced alongside code-based discounts
• Allocation breakdown showing how discounts are distributed

Allocation Methods:

• each - Applied independently per eligible item
• across - Split proportionally by value

Buyer Consent Extension

The buyer consent extension (dev.ucp.shopping.buyer_consent) enables platforms to transmit buyer consent choices regarding data usage and communication preferences.

Consent Categories:

• analytics - Data usage for analytics
• preferences - Personalization preferences
• marketing - Marketing communications
• sale_of_data - Data sale consent

This extension helps businesses comply with privacy regulations like CCPA and GDPR.

AP2 Mandates Extension

The AP2 mandates extension (dev.ucp.shopping.ap2_mandate) integrates the Universal Commerce Protocol with the AP2 Protocol for cryptographic proof of user authorization.

Key Features:

• Business provides cryptographic signature on checkout terms
• Platform provides cryptographically signed mandates proving user authorization
• Non-repudiable transaction evidence
• Support for Verifiable Digital Credentials (VDCs)
• SD-JWT with Key Binding format

Security Binding: Once this extension is negotiated, the session is security-locked. Neither party may revert to standard (unprotected) checkout flow.

Universal Commerce Protocol and Payment Architecture

The Universal Commerce Protocol adopts a decoupled payment architecture solving the "N-to-N" complexity between platforms, businesses, and payment credential providers.

Payment Handler Model

Payment handlers are specifications (not entities) that define how payment instruments are processed. They separate:

• Payment Instruments - What is accepted (card, wallet, etc.)
• Payment Handlers - How instruments are processed (tokenization specs)

Trust Triangle:

1. Business ↔ Payment Credential Provider - Pre-existing legal/technical relationship
2. Platform ↔ Payment Credential Provider - Platform tokenizes data but doesn't own funds
3. Platform ↔ Business - Platform passes token/mandate to business for finalization

Payment Lifecycle

The payment process follows a 3-step lifecycle:

1. Negotiation - Business advertises available handlers with configuration
2. Acquisition - Platform executes handler logic with payment credential provider
3. Completion - Platform submits opaque credential to business

Security Principles:

• Credentials flow Platform → Business only (unidirectional)
• Platforms handle tokens, not raw PANs (PCI-DSS scope minimization)
• Handler ID routing ensures correct key usage (prevents key confusion attacks)

PCI-DSS Scope Management

Platform Scope Minimization:

• Use handlers providing opaque credentials
• Never access or store raw payment data
• Forward credentials without ability to use directly

Business Scope Minimization:

• Use provider-hosted tokenization
• Use wallet providers with encrypted credentials
• Never log raw credentials
• Delegate to PCI-certified providers

Universal Commerce Protocol Schema Architecture

The Universal Commerce Protocol uses JSON Schema for data validation and self-describing capabilities. Understanding the schema architecture is crucial for implementing the Universal Commerce Protocol correctly.

Schema Categories

The Universal Commerce Protocol defines four schema categories:

Self-Describing Schemas

Capability schemas in the Universal Commerce Protocol MUST be self-describing. When a platform fetches a schema, it should determine exactly what capability and version it represents without cross-referencing other documents.

Why Self-Describing?

• Independent versioning - Capabilities can version independently
• Validation - Validators can cross-check capability declarations
• Developer experience - Immediate clarity on schema purpose
• Compact namespace - Reverse-domain identifiers (e.g., dev.ucp.shopping.checkout)

Schema Composition

Extensions in the Universal Commerce Protocol use allOf composition to extend base schemas:

{
  "$defs": {
    "checkout": {
      "allOf": [
        {"$ref": "checkout.json"},
        {
          "type": "object",
          "properties": {
            "discounts": {"$ref": "#/$defs/discounts_object"}
          }
        }
      ]
    }
  }
}

This composition model allows the Universal Commerce Protocol to maintain clean base schemas while supporting flexible extensions.

Universal Commerce Protocol Transport Layers

The Universal Commerce Protocol supports multiple transport protocols, enabling platforms and businesses to choose the best fit for their use case.

REST Transport (Primary)

The primary transport uses HTTP/1.1+ with RESTful patterns:

• Content-Type: application/json
• Standard HTTP verbs (POST, GET, PATCH)
• Standard HTTP status codes
• OpenAPI 3.x specification

Model Context Protocol (MCP)

UCP capabilities map 1:1 to MCP tools. Businesses can expose an MCP server wrapping their UCP implementation, allowing LLMs to call tools like create_checkout directly.

Agent-to-Agent Protocol (A2A)

Businesses can expose an A2A agent supporting UCP as an A2A Extension, enabling integration with platforms over structured UCP data types. The Universal Commerce Protocol integrates seamlessly with the A2A Protocol for agent-to-agent communication.

Embedded Protocol (EP)

Businesses can embed checkout interfaces that receive events as users interact, delegating key user actions. Initiation comes through a continue_url returned by the business.

Universal Commerce Protocol Integration with AP2 and A2A

Universal Commerce Protocol and AP2 Protocol

The Universal Commerce Protocol is fully compatible with the AP2 Protocol. AP2 serves as the trust layer for agent-led transactions, mandating secure, verifiable exchange of intents and authorizations.

Key Benefits:

• Binding proof - Cryptographic evidence of what was offered and agreed
• Fraud reduction - Payment mandates scoped to checkout hash, preventing token replay
• Agentic readiness - Allows autonomous AI agents to transact with verifiable boundaries

Protocol Flow:

1. Discovery - Business declares AP2 support
2. Session Activation - Platform signals AP2 activation
3. Signing (Business) - Business provides checkoutSignature (detached JWT)
4. Authorization - Platform generates CheckoutMandate and PaymentMandate
5. Completion - Platform submits mandates to /complete endpoint
6. Verification - Business and PSP verify mandates
7. Confirmation - Payment processed, order confirmed

Universal Commerce Protocol and A2A Protocol

The Universal Commerce Protocol integrates with the A2A Protocol for agent-to-agent communication. A2A enables agents to collaborate in their natural modalities, while UCP provides the commerce-specific primitives.

Complementary Roles:

• A2A Protocol - Application-level protocol for agent collaboration
• Universal Commerce Protocol - Commerce-specific capabilities and data models

Together, they enable AI agents to discover businesses, negotiate checkout terms, and complete purchases autonomously.

Getting Started with Universal Commerce Protocol

For Developers

The Universal Commerce Protocol provides comprehensive resources for developers:

1. Technical Specification - Complete protocol documentation at ucp.dev
2. GitHub Repository - Open-source implementation and samples at github.com/Universal-Commerce-Protocol/ucp
3. Code Samples - Reference implementations in multiple languages
4. Playground - Interactive demo at ucp.dev/playground

For Businesses

Businesses can integrate the Universal Commerce Protocol to:

• Meet customers wherever they are (AI assistants, shopping agents, embedded experiences)
• Remain the Merchant of Record with full ownership of customer relationships
• Retain control of business rules and logic
• Avoid rebuilding checkout for each platform

Integration Steps:

1. Implement UCP profile at /.well-known/ucp
2. Support core capabilities (checkout, order)
3. Add extensions as needed (fulfillment, discounts)
4. Configure payment handlers
5. Set up webhook endpoints for order events

For AI Platforms

AI platforms can use the Universal Commerce Protocol to:

• Simplify business onboarding with standardized APIs
• Provide integrated shopping experiences
• Support multiple transport protocols (REST, MCP, A2A)
• Enable autonomous agent commerce with AP2 integration

For Payment Providers

Payment providers can:

• Define payment handler specifications
• Publish handler schemas and configurations
• Support multiple payment instruments
• Integrate with AP2 for cryptographic mandates

Universal Commerce Protocol Roadmap

The Universal Commerce Protocol follows a phased development approach with upcoming priorities:

Deeper Support for Full Consumer Journey

Expanding beyond isolated transactions to support:

• Product discovery - Facilitating entire shopping journey
• Cart and basket building - Multi-item checkout with complex rules
• Loyalty & Member benefits - Account linking and personalized offers
• Native cross-sell and upsell - Personalized recommendations

Support for Global Markets

Phased rollout across markets including:

• India
• Indonesia
• Latin America
• Other regional markets

Adapting the Universal Commerce Protocol to support broader regional use cases and localized payment interoperability.

Community-Driven Evolution

The Universal Commerce Protocol is built by the industry, for the industry. The roadmap reflects strategic priorities but remains flexible based on community feedback and business needs.

🤔 Common Questions About Universal Commerce Protocol

Q: What makes Universal Commerce Protocol different from other commerce APIs?

A: The Universal Commerce Protocol is designed specifically for agentic commerce and interoperability. Unlike proprietary APIs, UCP provides:

• Standardized capability discovery and negotiation
• Multiple transport protocol support (REST, MCP, A2A)
• Built-in security with AP2 integration
• Extension model for flexible feature addition
• Open standard with industry-wide adoption

Q: How does Universal Commerce Protocol ensure security?

A: The Universal Commerce Protocol implements multiple security layers:

• OAuth 2.0 for identity linking
• PCI-DSS compliant payment patterns
• AP2 Protocol integration for cryptographic mandates
• JWT-based webhook signatures
• Unidirectional credential flow (Platform → Business only)

Q: Can Universal Commerce Protocol work with existing payment systems?

A: Yes. The Universal Commerce Protocol is designed to work with existing payment infrastructure:

• Supports all major payment methods (cards, wallets, bank transfers, crypto)
• Integrates with existing PSPs (Stripe, Adyen, PayPal, etc.)
• Doesn't require changes to existing risk/fraud systems
• Provides additional signals for better risk assessment

Q: What is the relationship between Universal Commerce Protocol, AP2, and A2A?

A: These protocols are complementary:

• Universal Commerce Protocol - Commerce-specific capabilities and data models
• AP2 Protocol - Trust layer for agent payments with cryptographic mandates
• A2A Protocol - Agent-to-agent communication protocol

UCP integrates AP2 for secure payments and can use A2A as a transport layer.

Q: How do businesses get started with Universal Commerce Protocol?

A: Businesses can start by:

1. Reviewing the technical specification at ucp.dev
2. Implementing the UCP profile endpoint (/.well-known/ucp)
3. Supporting core capabilities (checkout, order)
4. Testing with the UCP Playground
5. Integrating with platforms supporting the Universal Commerce Protocol

Q: What programming languages are supported for Universal Commerce Protocol?

A: The Universal Commerce Protocol is language-agnostic. It uses:

• JSON for data exchange
• Standard HTTP for REST transport
• JSON-RPC for MCP/A2A transports
• OpenAPI/OpenRPC specifications

Reference implementations are available in Python and TypeScript, with community contributions in other languages.

Q: How does Universal Commerce Protocol handle schema versioning?

A: The Universal Commerce Protocol uses date-based versioning (YYYY-MM-DD) for schemas:

• Each capability schema declares its version in the version field
• Schemas are self-describing with name and version fields
• Platforms validate schema URLs match namespace authorities
• Independent versioning allows capabilities to evolve at different rates

Q: What is the namespace governance model in Universal Commerce Protocol?

A: The Universal Commerce Protocol uses reverse-domain naming:

• UCP capabilities: dev.ucp.* namespace (governed by UCP body)
• Vendor capabilities: com.{vendor}.* namespace (vendor-controlled)
• No central registry needed - DNS-based namespace governance
• Spec URLs must match namespace authority origins

Q: How does Universal Commerce Protocol handle versioning?

A: The Universal Commerce Protocol uses date-based versioning (YYYY-MM-DD format):

• Protocol versions independently from capabilities
• Each capability versions independently
• Strong backwards compatibility guarantees
• Clear breaking change policies

Q: Can vendors extend Universal Commerce Protocol?

A: Yes. The Universal Commerce Protocol supports vendor capabilities:

• Vendors use reverse-domain namespace (e.g., com.shopify.loyalty)
• Vendor capabilities version independently
• Same self-describing schema requirements
• No central registry needed

Q: What is the difference between capabilities and extensions in Universal Commerce Protocol?

A: In the Universal Commerce Protocol:

• Capabilities - Standalone core features (checkout, order, identity linking)
• Extensions - Optional features that augment capabilities (fulfillment extends checkout)

Extensions use the extends field to declare their parent capability and are automatically pruned if the parent isn't in the capability intersection.

Q: How does Universal Commerce Protocol support AI agents?

A: The Universal Commerce Protocol enables AI agents through:

• Capability discovery for dynamic business feature detection
• Programmatic checkout flows with error handling
• AP2 integration for autonomous transactions with cryptographic proof
• Multiple transport options (REST, MCP, A2A) for different agent frameworks
• Structured data models optimized for agent processing

Summary and Next Steps

The Universal Commerce Protocol (UCP) represents a fundamental shift toward standardized, interoperable commerce. By providing a common language for platforms, businesses, and payment providers, the Universal Commerce Protocol eliminates the need for custom integrations while enabling true agentic commerce.

Key Advantages of Universal Commerce Protocol

Recommended Next Steps

1. Explore the Specification - Review the complete technical documentation at ucp.dev/specification
2. Try the Playground - Experiment with the interactive demo at ucp.dev/playground
3. Review Code Samples - Check out reference implementations at github.com/Universal-Commerce-Protocol/samples
4. Join the Community - Contribute feedback and code at github.com/Universal-Commerce-Protocol/ucp

The Universal Commerce Protocol is actively evolving with community input. Whether you're a developer building the next generation of commerce experiences, a business looking to reach customers everywhere, or a payment provider enabling secure transactions, the Universal Commerce Protocol provides the foundation for interoperable, agentic commerce.

Related Resources:

• AP2 Protocol Documentation - Secure payments for the Agent Economy
• A2A Protocol Documentation - Agent-to-Agent communication standard
• Universal Commerce Protocol GitHub - Open-source implementation
• Universal Commerce Protocol Specification - Complete technical documentation
• Universal Commerce Protocol Guide - Comprehensive guide to the Universal Commerce Protocol