# Universal Commerce Protocol (UCP) > The Universal Commerce Protocol (UCP) is a solution for enabling gen AI agents to make payments on behalf of users, safely, securely, and in a decentralized and privacy protecting manner. This protocol is a part of the broader ecosystem, which includes agentic protocols like A2A and MCP, and encompasses the global nature of payments. This is the documentation directory for the Universal Commerce Protocol (UCP), an open standard that enables gen AI agents to safely, securely, and privately execute commerce actions (i.e., discovering, buying) on behalf of users. ### Technical Specification Indices (llms.txt) For raw, LLM-optimized indices of our versioned technical specifications: - [Latest Stable UCP Specification Index](https://ucp.dev/latest/llms.txt): Standardized specifications for production deployments. - [UCP Specification Index (2026-04-08)](https://ucp.dev/2026-04-08/llms.txt): Stable spec release version 2026-04-08. - [UCP Specification Index (2026-01-23)](https://ucp.dev/2026-01-23/llms.txt): Stable spec release version 2026-01-23. - [UCP Specification Index (2026-01-11)](https://ucp.dev/2026-01-11/llms.txt): Stable spec release version 2026-01-11. ## Specification - [Overview](http://ucp.dev/2026-08-25/specification/overview/index.md): Master technical specification of UCP, discovery mechanisms, secure transports, capability negotiation, and error taxonomies. - [Glossary](http://ucp.dev/2026-08-25/specification/glossary/index.md): Definitions of the protocol, commerce, payment, regulatory, and standards terms and acronyms used throughout the specification, including Capability, Extension, Action, Platform, Business, and Merchant of Record. ## Common - [Identity Linking](http://ucp.dev/2026-08-25/specification/common/identity-linking/index.md): User authentication via the Identity Linking Capability, specifying direct B2C/B2B OAuth 2.0 flows (with PKCE and RFC 9207) to unlock personalized commerce data. - [Loyalty](http://ucp.dev/2026-08-25/specification/common/extensions/loyalty/index.md): Loyalty Extension, enabling high-fidelity member benefit recognition during catalog, cart, and checkout by defining schemas for memberships, tiers, benefits, and reward earning forecasts while managing provisional eligibility claims and enforcing data-minimization privacy rules. ## Location Capability - [Overview](http://ucp.dev/2026-08-25/specification/common/location/index.md): Core Location Capability, detailing physical Location discovery, spatial relations, item availability, operating hours, and amenities. - [Search](http://ucp.dev/2026-08-25/specification/common/location/search/index.md): Location discovery via the Location Search capability, specifying text queries, spatial relations, and structured filters. - [Lookup](http://ucp.dev/2026-08-25/specification/common/location/lookup/index.md): Direct Location retrieval via the Location Lookup capability, specifying identifiers and optional spatial relations and filters. - [REST](http://ucp.dev/2026-08-25/specification/common/location/rest/index.md): HTTP REST transport binding for the Location Capability, detailing search and lookup endpoints with JSON payload examples. - [MCP](http://ucp.dev/2026-08-25/specification/common/location/mcp/index.md): Model Context Protocol (MCP) transport binding for the Location Capability, mapping discovery operations to JSON-RPC tools with metadata validation rules. ## Message Signatures - [Signatures](http://ucp.dev/2026-08-25/specification/signatures/index.md): Implementation details for RFC 9421 HTTP Message Signatures and RFC 9530 Content-Digests to achieve secure, transport-agnostic request authentication and replay protection. ## Checkout Capability - [Overview](http://ucp.dev/2026-08-25/specification/shopping/checkout/index.md): Core Checkout Capability specifications detailing session state lifecycles, totals calculation rules, and buyer input validation severity states. - [REST](http://ucp.dev/2026-08-25/specification/shopping/checkout/rest/index.md): HTTP REST transport binding for Checkout operations, specifying standard headers, API endpoints, status codes, and payload structures. - [MCP](http://ucp.dev/2026-08-25/specification/shopping/checkout/mcp/index.md): Model Context Protocol (MCP) transport binding for Checkout operations, mapping UCP capabilities to JSON-RPC tools with agent metadata rules. - [A2A](http://ucp.dev/2026-08-25/specification/shopping/checkout/a2a/index.md): Agent2Agent Protocol (A2A) binding for Checkout Capability, detailing transport discovery, agent card profile advertisement, and message negotiation flows. - [Embedded protocol](http://ucp.dev/2026-08-25/specification/embedded-protocol/index.md): Core Embedded Protocol (EP) transport binding, defining message formats, handshake patterns, communication channels, security constraints, and shared error handling structures for iframe/webview integrations. - [Embedded](http://ucp.dev/2026-08-25/specification/shopping/checkout/embedded/index.md): Embedded Checkout Protocol (ECP) specification, detailing per-session delegation negotiation, URL parameters, native UI event mappings, W3C Payment Request conceptual alignment, and core lifecycle messages. ## Cart Capability - [Overview](http://ucp.dev/2026-08-25/specification/shopping/cart/index.md): Pre-purchase Cart Capability, detailing item collection, state modification, and seamless transition handoff to active checkout sessions. - [REST](http://ucp.dev/2026-08-25/specification/shopping/cart/rest/index.md): HTTP REST transport binding for Cart operations, including endpoints for session creation, modification, retrieval, and cancellation. - [MCP](http://ucp.dev/2026-08-25/specification/shopping/cart/mcp/index.md): Model Context Protocol (MCP) transport binding for Cart operations, mapping item management to JSON-RPC tools for AI shopping agents. - [Embedded protocol](http://ucp.dev/2026-08-25/specification/embedded-protocol/index.md): Core Embedded Protocol (EP) transport binding, defining message formats, handshake patterns, communication channels, security constraints, and shared error handling structures for iframe/webview integrations. - [Embedded](http://ucp.dev/2026-08-25/specification/shopping/cart/embedded/index.md): Embedded Cart Protocol (ECaP), enabling secure, cross-origin iframe communication and synchronized event states between platform agents and business websites. ## Permalink Capability - [Permalink Capability](http://ucp.dev/2026-08-25/specification/permalink/index.md): Browser-addressable shopping intent capability, defining endpoint discovery, compact item paths, open query initialization fields, and redirect resolution. ## Catalog Capability - [Overview](http://ucp.dev/2026-08-25/specification/shopping/catalog/index.md): Core Catalog Capability, detailing high-level product discovery models, variant structures, merchant attribution, and real-time pricing context. - [Search](http://ucp.dev/2026-08-25/specification/shopping/catalog/search/index.md): Product discovery via the Search Catalog capability, specifying text queries, category browsing, and multi-attribute filtering contracts. - [Lookup](http://ucp.dev/2026-08-25/specification/shopping/catalog/lookup/index.md): Direct item retrieval via the Lookup Catalog capability, specifying variant resolution logic, batch identifiers, and interactive option selection. - [REST](http://ucp.dev/2026-08-25/specification/shopping/catalog/rest/index.md): HTTP REST transport binding for the Catalog Capability, detailing search, batch lookup, and product detail endpoints with JSON payload examples. - [MCP](http://ucp.dev/2026-08-25/specification/shopping/catalog/mcp/index.md): Model Context Protocol (MCP) transport binding for the Catalog Capability, mapping discovery operations to JSON-RPC tools with metadata validation rules. ## Order Capability - [Overview](http://ucp.dev/2026-08-25/specification/shopping/order/index.md): Post-purchase tracking via the Order Capability, detailing line item updates, fulfillment expectations, shipment events, adjustments, and webhook-based status updates. - [REST](http://ucp.dev/2026-08-25/specification/shopping/order/rest/index.md): HTTP REST transport binding for the Order Capability, detailing endpoints, HTTP headers, payload schemas, and error structures. - [MCP](http://ucp.dev/2026-08-25/specification/shopping/order/mcp/index.md): Model Context Protocol (MCP) transport binding for the Order Capability, detailing the JSON-RPC tool interface and parameters for fetching order states. ## Shopping Extensions - [Fulfillment](http://ucp.dev/2026-08-25/specification/shopping/extensions/fulfillment/index.md): Fulfillment extension for checkouts, defining delivery methods, pickup destinations, and method-agnostic UI rendering contracts. - [Discounts](http://ucp.dev/2026-08-25/specification/shopping/extensions/discount/index.md): Discount Extension, covering discount code discovery, applied discounts, allocation method stacking orders, rejected code message handling, and automatic or provisional eligibility promotions. - [Buyer Consent](http://ucp.dev/2026-08-25/specification/shopping/extensions/buyer-consent/index.md): Buyer Consent Extension, defining data schemas for transmitting buyer privacy choices (analytics, marketing, personalization) to assist with privacy compliance (CCPA/GDPR). ## Payment - [AP2 Mandates Extension](http://ucp.dev/2026-08-25/specification/payment/extensions/ap2-mandates/index.md): AP2 Mandates Extension, detailing secure, cryptographically bound checkout commitments (using SD-JWT+kb digital credentials and detached JWS signatures) between business, platform, and payment providers. - [Overview](http://ucp.dev/2026-08-25/specification/payment/extensions/authentication/index.md): Payment Authentication Extension, defining negotiation, payment-handler association, lifecycle, trust, and embedded notifications for standard payment authentication Actions. - [Device Data Collection](http://ucp.dev/2026-08-25/specification/payment/extensions/actions/device-data-collection/index.md): Standard Action type for running invisible device-data collection surfaces during payment processing. - [3DS Challenge](http://ucp.dev/2026-08-25/specification/payment/extensions/actions/three-ds-challenge/index.md): Standard Action type for presenting buyer-facing 3DS challenges. - [Split Payments Extension](http://ucp.dev/2026-08-25/specification/payment/extensions/split-payments/index.md): Split Payments Extension, defining multiple payment instrument allocation, settlement rules, and amount distribution across payment handlers. - [Payment Terms Extension](http://ucp.dev/2026-08-25/specification/payment/extensions/terms/index.md): Payment Terms Extension, enabling checkout payment schedules for immediate and deferred payments such as deposits, installments, and lodging balance-at-check-in flows. - [Guide](http://ucp.dev/2026-08-25/specification/payment/guide/index.md): Architectural framework and standard vocabulary for specifying UCP payment handlers, covering configuration declarations and transaction execution. - [Template](http://ucp.dev/2026-08-25/specification/payment/template/index.md): Standard Markdown template and integration checklist when authoring new UCP payment handler specifications. - [Tokenization Guide](http://ucp.dev/2026-08-25/specification/payment/tokenization/index.md): Shared API, security requirements, and lifecycle policies (single-use, TTL, session-scoped) for building compliant tokenization payment handlers. - [Processor Tokenizer](http://ucp.dev/2026-08-25/specification/payment/examples/processor-tokenizer-payment-handler/index.md): Concrete payment handler example utilizing a 'Tokenize to Process' flow, where a single enterprise vault or PSP tokenizes credentials and resolves them internally. - [Platform Tokenizer](http://ucp.dev/2026-08-25/specification/payment/examples/platform-tokenizer-payment-handler/index.md): Concrete payment handler example utilizing a 'Platform-as-Tokenizer' flow, where a platform's wallet generates tokens and hosts a secure detokenization endpoint. - [Encrypted Credential](http://ucp.dev/2026-08-25/specification/payment/examples/encrypted-credential-payment-handler/index.md): Concrete payment handler example utilizing a 'Direct Encryption' flow, where a platform encrypts payment data with a business's public key for local decryption. ## Reference & Tooling - [Reference](http://ucp.dev/2026-08-25/specification/reference/index.md): Complete reference directory of all core UCP, type, and extension JSON schemas, including platform/business profiles and metadata objects. - [Playground](http://ucp.dev/2026-08-25/specification/shopping/playground/index.md): Interactive, browser-based UCP Playground simulator for walking through step-by-step checkout sessions, payment handling, and backend webhooks.