Guide

    UCP vs ACP vs MCP vs AP2: what each does and what a brand needs

    A plain comparison of the four agentic commerce protocols — UCP, ACP, MCP and AP2 — what each one covers and which a brand actually needs.

    The Apirro team

    MCP lets AI assistants call tools and read data. UCP is a commerce protocol for catalogue, cart and checkout across agents. ACP is a checkout protocol used for purchases inside ChatGPT. AP2 covers how an agent proves it is authorised to pay. Most brands need readable data and MCP or UCP first.

    MCP — Model Context Protocol

    MCP is an open standard for connecting AI assistants to external tools and data. For a store, an MCP server can expose tools such as search products, get product and create cart. Claude, ChatGPT developer tools, Cursor and many other clients can connect to MCP servers.

    MCP is general-purpose: it says how an assistant calls a tool, not what a commerce cart or checkout should look like.

    UCP — Universal Commerce Protocol

    UCP is an open commerce protocol that defines a shared shape for catalogue search, carts and checkout sessions, plus a discovery profile at /.well-known/ucp. It can be served over REST or bound to MCP. Google uses it for shopping in AI Mode and Gemini.

    ACP — Agentic Commerce Protocol

    ACP is an open checkout specification developed by OpenAI and Stripe. It describes how an agent such as ChatGPT creates and completes a checkout with a merchant, with payment credentials passed through the merchant's payment provider. Merchants typically take part through an approved programme and a product feed.

    Whether a brand needs ACP depends on whether it wants purchases to complete inside ChatGPT.

    AP2 — Agent Payments Protocol

    AP2 is about trust in payment, not product data. It defines signed mandates that show a shopper authorised an agent to buy something within set limits, so merchants and payment providers can verify the request.

    What a brand needs, in order

    • Clean, structured product data with live price and stock — every protocol depends on it.
    • Discovery files so agents can find your endpoints.
    • An MCP and/or UCP endpoint so assistants can search and build carts.
    • A checkout path you control; add ACP or AP2 where the assistants and payment providers you rely on require them.

    FAQ

    Are these protocols competing?

    Partly overlapping, mostly complementary. MCP is transport for tools, UCP and ACP describe commerce flows, and AP2 handles payment authorisation. A single brand can support several at once.

    Does Apirro support all four?

    Apirro's Agent Link™ publishes MCP and UCP endpoints and an AP2 discovery file today. ACP is described here for comparison; check the Agent Link pages for the current list of supported protocols.

    Which one should a small brand start with?

    Start with accurate product data and one agent endpoint (MCP or UCP). That makes the catalogue usable by most assistants before you take on checkout-specific programmes.

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