What Is the Universal Commerce Protocol (UCP)?
> The Universal Commerce Protocol (UCP) is an open standard for agentic commerce that enables AI agents to discover merchant capabilities, search product catalogs, manage cart sessions, complete checkout, and handle post-purchase flows — covering the entire shopping lifecycle through a standardised, machine-readable protocol that any compatible platform or merchant can implement.
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What Is UCP?
The Universal Commerce Protocol (UCP) is an open standard for connecting AI agents with merchant commerce systems. It was co-developed by Google with a broad coalition of retail partners including Shopify, Etsy, Wayfair, Target, and Walmart, and has since been endorsed by more than 60 organisations. The goal of UCP is to define a common language for commerce — one that lets AI agents interact with any merchant as a programmable service rather than as a website to be browsed, form to be filled, or API to be custom-integrated.
Google's support documentation describes UCP as a new open standard for agentic commerce that enables agents and systems to work together across the commerce ecosystem. The official UCP site at ucp.dev describes the protocol as designed to facilitate the entire commerce lifecycle, from initial product discovery and search to final sale and post-purchase support. This full-lifecycle scope is what distinguishes UCP from narrower protocols: rather than defining only a checkout flow or only a product feed format, UCP defines a complete interaction model — from the moment an AI agent first queries a merchant to the moment an order is fulfilled.
UCP is transport-agnostic and extensible. It supports REST as the primary transport but is also compatible with MCP (Model Context Protocol) and A2A (Agent-to-Agent) frameworks, allowing it to work within different AI agent architectures without requiring protocol-level changes.
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How UCP Works
UCP operates through a three-layer architecture: discovery, capability negotiation, and service execution.
Discovery. Every UCP-enabled merchant publishes a machine-readable JSON manifest at the `/.well-known/ucp` endpoint on their domain. This manifest is the entry point for every agent interaction. When an AI agent wants to interact with a merchant, it fetches this manifest to learn what the merchant supports — which capabilities are available, which service endpoints are active, what versions are in use, and what payment handlers are configured. This standard discovery location follows IETF well-known URI conventions, making it predictable for any agent platform to query without custom integration.
Capability negotiation. After fetching the manifest, the agent computes the intersection of capabilities supported by both the agent platform and the merchant — what the UCP specification describes as the "server-selects" algorithm. This negotiation step means that a merchant does not need to support every UCP capability to participate in the protocol; they declare what they support, and the agent works within those declared capabilities. A merchant that supports only search and lookup can still be discovered and evaluated; one that also supports cart and checkout can complete purchases.
Service execution. Once capabilities are negotiated, the agent calls the merchant's service endpoints to execute commerce actions: search the catalog, look up a product by barcode, create a cart, add items, initiate checkout, link a buyer identity, or query order status. Each capability is a defined service with a specified API contract that the merchant implements on their own infrastructure.
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Key Components of UCP
| Component | Description | Source | |---|---|---| | `/.well-known/ucp` manifest | Machine-readable JSON declaring merchant capabilities, endpoints, and payment handlers | UCP Spec | | Catalog Search API (`POST`) | Free-text product search with filters and cursor-based pagination | UCP Spec / FeedBridge | | Catalog Lookup API (`POST`) | Retrieve specific products by `item_id` or barcodes (GTIN/MPN) | UCP Spec / FeedBridge | | Cart API (`POST`) | Create, update, get, and checkout multi-item cart sessions | UCP Spec / FeedBridge | | Identity Linking API (`POST`) | Link/unlink buyer accounts using OAuth 2.0; JWT assertions for intent checks | UCP Spec / FeedBridge | | Redirect Checkout | Standard checkout redirect with privacy and ToS URLs | UCP Spec / FeedBridge | | UCP Profile | Business profile declaring supported services and capabilities | UCP Spec | | AP2 Extension | Cryptographic proof layer for verifiable agent transactions | UCP / AP2 Spec |
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UCP's Full Commerce Lifecycle Coverage
One of UCP's defining characteristics is its scope. Most existing commerce protocols — EDI, product feed formats, payment APIs — address one phase of the commerce journey. UCP is designed to cover all phases:
- Discovery: Agents fetch the `/.well-known/ucp` manifest to learn what the merchant supports
- Search: Agents query the Catalog Search API to find products matching a buyer's intent
- Lookup: Agents retrieve specific product details by identifier or barcode
- Cart: Agents create and manage multi-item shopping cart sessions
- Checkout: Agents initiate and complete purchases, either via redirect or native checkout
- Identity: Agents link a buyer's account with the merchant for personalised experiences
- Post-purchase: Order status, fulfilment tracking, and return flows (as supported capabilities)
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Interoperability with Adjacent Protocols
UCP is explicitly designed to work alongside, not instead of, other protocols in the AI ecosystem:
MCP (Model Context Protocol): UCP supports MCP as a transport layer, meaning UCP commerce capabilities can be exposed as MCP tools. This allows AI agents built on MCP-compatible frameworks to invoke UCP commerce actions (search, cart, checkout) as native tool calls, without requiring a separate REST client.
A2A (Agent-to-Agent): UCP supports the A2A communication framework, allowing UCP-defined commerce services to be orchestrated by multi-agent systems where one agent delegates commerce tasks to another.
AP2 (Agent Payments Protocol): UCP is deeply integrated with AP2, which acts as a cryptographic trust layer on top of UCP's commerce capabilities. AP2 adds digital signatures — `CheckoutMandate` and `PaymentMandate` — that provide verifiable proof of user intent and payment authorisation. This integration is relevant for high-value transactions or contexts where cryptographic non-repudiation is required.
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Why It Matters for Merchants
UCP changes the addressable surface for merchant discoverability. In the traditional web commerce model, a merchant is discoverable to the extent that their website ranks in search engines or their ads appear in the right places. In the UCP model, a merchant is discoverable to any AI agent that queries their `/.well-known/ucp` manifest — which means discoverability is determined by protocol implementation, not by SEO or ad spend.
Once a merchant is UCP-enabled and listed in Google AI Mode via Merchant Center, their products become available for AI-assisted purchasing on Google's AI surfaces (Search, Gemini). The `native_commerce` product attribute in Google Merchant Center — when set to `true` — signals that a product is eligible for the UCP-powered purchase experience. This is a product-level attribute, meaning merchants can choose which products participate while others remain on standard Google Shopping.
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FeedBridge Relevance
FeedBridge implements the full UCP REST protocol stack as of April 2026. This includes the machine-readable `/.well-known/ucp` manifest, Catalog Search API (POST, free-text search with filters and pagination), Catalog Lookup API (POST, by `item_id` or barcodes), Cart API (create, update, get, checkout multi-item sessions), Identity Linking API (link/unlink buyer accounts, OAuth 2.0 stub), and Redirect Checkout (auto-enabled with privacy and ToS URLs).
The FeedBridge UCP Dashboard Hub provides merchants with a compliance scorecard and capability checklist, so they can see exactly which UCP capabilities are active and which are missing from their implementation. An API Playground in the dashboard allows merchants to test Catalog Search, Catalog Lookup, and Cart responses in-dashboard before exposing them to AI agents. FeedBridge also generates Google Merchant Center CSV exports that support the feed submission step of UCP onboarding via Merchant Center.
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Frequently Asked Questions
Q: Is UCP the same as ACP? A: No. UCP (Universal Commerce Protocol) and ACP (Agentic Commerce Protocol) are distinct open standards. UCP was co-developed by Google and covers the full commerce lifecycle from discovery through post-purchase. ACP was developed with OpenAI and Stripe and focuses specifically on the checkout and payment delegation flow within AI surfaces like ChatGPT. They address different AI surfaces and can be implemented independently or in parallel.
Q: Which AI surfaces use UCP? A: UCP is the protocol for Google AI Mode and Gemini. Merchants who want their products purchasable through Google's AI-powered shopping surfaces must implement UCP and onboard through Google Merchant Center.
Q: Do I need to implement every UCP capability? A: No. UCP uses a capability declaration model. A merchant declares which capabilities they support in their manifest, and the agent works within those declared capabilities. Merchants can start with basic search and lookup and add cart, checkout, and identity linking progressively.
Q: Is UCP free to implement? A: Yes. UCP is an open standard with freely available specification documentation at ucp.dev. There are no licensing costs. Standard infrastructure costs (hosting, PSP transaction fees) apply as with any commerce integration.
Q: How does UCP relate to the `native_commerce` attribute in Merchant Center? A: The `native_commerce` attribute is a product-level boolean in the Google Merchant Center feed that signals a product's eligibility for the UCP-powered purchase experience on Google surfaces. Products with `native_commerce: true` are eligible for AI-assisted purchasing; those without it remain on the standard Google Shopping experience.
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Related Topics
Parent hub: UCP Foundations
Related concepts:
- How UCP Powers Agentic Checkout
- UCP Across the Full Shopping Journey
- UCP Capability Discovery Explained
- UCP Profile and Capability Negotiation Basics
- UCP Identity Linking Overview
- UCP Merchant Center Onboarding Explained
Breadcrumb:
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Source Documentation
| Claim | Source | Source Class | Reference | |---|---|---|---| | UCP co-developed by Google with Shopify, Etsy, Wayfair, Target, Walmart; endorsed by 60+ organisations | a2aprotocol.ai UCP guide | T1 – Official UCP Docs | https://a2aprotocol.ai/blog/2026-universal-commerce-protocol | | UCP covers full commerce lifecycle: discovery through post-purchase | ucp.dev | T1 – Official UCP Docs | http://ucp.dev | | `/.well-known/ucp` manifest; server-selects negotiation algorithm | Google Developers Blog / stellagent.ai | T1 – Official UCP Docs | https://developers.googleblog.com/under-the-hood-universal-commerce-protocol-ucp/ | | UCP supports MCP and A2A as transports | a2aprotocol.ai UCP guide | T1 – Official UCP Docs | https://a2aprotocol.ai/blog/2026-universal-commerce-protocol | | AP2 integration: CheckoutMandate, PaymentMandate | ucp.md AP2 integration docs | T1 – Official UCP Docs | https://ucp.md/en/docs/ap2-integration/ | | `native_commerce` attribute in Merchant Center | almcorp.com UCP Merchant Center explainer | T2 – Platform Partner Docs | https://almcorp.com/blog/google-universal-commerce-protocol-ucp-explained/ | | FeedBridge UCP full REST stack: manifest, search, lookup, cart, identity, redirect checkout | FeedBridge Platform Capabilities April 2026 v2.0 | T1 – FeedBridge Internal | FeedBridge-Platform-Capabilities-April2026.md |