Protocol Specification

Specification Reading Guide

The specification documents on this site don’t copy the official text. Instead, from an engineering implementation perspective, they break down the specification into actionable checklists:

• What you need to declare (Profile / Capabilities / Endpoints)?
• What you need to verify (namespace & spec origin binding, Schema composition, extension dependencies)?
• What you need to implement (minimum bindings for REST/MCP/A2A/Embedded)?

Specification Structure

Core Specifications

• Specification Overview: Namespace governance, capability negotiation, version control
• Discovery & Negotiation: Profile structure, capability intersection algorithm
• Transport Layer: REST/MCP/A2A/Embedded binding specifications

Capability Specifications

• Checkout Capability: Checkout session management, status lifecycle
• Identity Linking: OAuth 2.0 identity linking
• Order Capability: Order lifecycle event notifications

Extension Specifications

• Fulfillment Extension: Delivery fulfillment
• Discount Extension: Discount offers
• AP2 Mandates Extension: Encrypted payment instructions
• Buyer Consent Extension: Buyer consent and data preferences

Draft Specifications

The following capabilities are under active development:

• Cart Capability (DRAFT): Basket building before checkout
• Catalog Capability (DRAFT): Product discovery and search

Payment Specifications

• Payment Handler Guide: Payment processor specification
• Tokenization Guide: Payment token exchange

Canonical Sources

All technical details on this site are subject to the official specifications:

• Official specification: https://ucp.dev/specification/overview
• Official repository: github.com/Universal-Commerce-Protocol/ucp

Keywords Notice

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, OPTIONAL in the specification are to be interpreted as described in RFC 2119 and RFC 8174.

Schema Notice

• Date format: RFC 3339, unless otherwise specified
• Amount format: Minimum unit (cents)

Version Notice

This document is based on UCP Protocol version 2026-01-11.