Protocol Overview

What is UCP?

UCP addresses fragmentation in modern commerce by providing a standardized common language and functional primitives. It enables AI agents, platforms, and businesses to communicate seamlessly without custom integrations for each combination.

Think of UCP as the "HTTP of commerce" - just as HTTP standardized web communication, UCP standardizes commerce operations across all participants in the ecosystem.

Design Principles

Standardized Interoperability

Uniform way for platforms to interact regardless of backend systems

Modular Architecture

Distinct Capabilities (core) and Extensions (optional augmentations)

Agentic Commerce

Designed for AI agents acting autonomously on behalf of users

Security & Compliance

Built on OAuth 2.0, cryptographic proofs, and PCI-DSS patterns

Protocol Layers

1. Capabilities Layer

Capabilities are the fundamental building blocks that define core commerce operations. Every UCP-compatible system must support these:

Checkout (dev.ucp.shopping.checkout) - Create and complete purchase sessions
Identity Linking (dev.ucp.common.identity_linking) - OAuth 2.0 user authorization
Order (dev.ucp.shopping.order) - Lifecycle management and tracking

2. Extensions Layer

Extensions are optional augmentations that add specialized functionality:

Fulfillment (dev.ucp.shopping.fulfillment) - Shipping, pickup, delivery options
Discount (dev.ucp.shopping.discount) - Promotional codes and automatic discounts
AP2 Mandates (dev.ucp.common.ap2_mandate) - Cryptographic authorization proofs
Buyer Consent (dev.ucp.common.buyer_consent) - Privacy compliance (GDPR, CCPA)

3. Transport Layer

Transports define communication protocols for different integration scenarios:

REST - HTTP/HTTPS primary transport for direct API calls
MCP - Model Context Protocol for LLM tool integration
A2A - Agent-to-Agent communication for autonomous operations
Embedded - iframe/webview integration for hybrid experiences

Business Profile Declaration

Every UCP-compatible business declares a machine-readable profile that describes its capabilities and endpoints. This profile is served at a well-known URL:

GET /.well-known/ucp/business_profile.json

{
  "identifier": "urn:ucp:business:acme-store",
  "name": "ACME Store",
  "protocol_version": "1.0",
  "capabilities": [
    "dev.ucp.shopping.checkout",
    "dev.ucp.common.identity_linking",
    "dev.ucp.shopping.order"
  ],
  "extensions": [
    "dev.ucp.shopping.fulfillment",
    "dev.ucp.shopping.discount"
  ],
  "transports": {
    "rest": {
      "base_url": "https://api.acme-store.com/ucp/v1"
    },
    "mcp": {
      "server_url": "https://mcp.acme-store.com"
    }
  }
}

Transaction Flow

A typical UCP transaction follows these steps:

Discovery - Agent discovers business profile via well-known URL
Capability Check - Agent verifies required capabilities are supported
Session Creation - Agent creates a checkout session
Cart Management - Products are added/modified in the cart
Payment - Payment is processed via configured handler
Confirmation - Order is confirmed and tracking begins

Next Steps

Explore the Capabilities section to learn about core commerce operations, or dive into Transports to understand communication protocols.