ACP, UCP, AP2 & MCP — the agentic protocol stack

Four open protocols make a store buyable by an AI agent. They are complementary, not competing — a fully agent-ready store serves all four. This is the plain-English version; each links to its specification.

ACP — Agentic Commerce Protocol

Backed by: OpenAI · Stripe
What it does: Lets an agent (e.g. ChatGPT) discover your catalogue and complete a purchase against your checkout, with a signed receipt back to the merchant.
You serve: a product feed plus a checkout endpoint the agent can drive.
Spec: https://www.agenticcommerce.dev/

UCP — Universal Commerce Protocol

Backed by: Google · Shopify
What it does: The authoritative discovery profile. A single document at /.well-known/ucp that declares which protocols your store supports and the endpoint URLs for each — the map every other agent reads first.
You serve: a UCP profile listing your services and capabilities.
Spec: https://ucp.dev/

AP2 — Agent Payments Protocol

Backed by: Google · Visa · Mastercard · PayPal (60+ organisations)
What it does: Cryptographic payment authorisation so an agent can pay with a verifiable, signed mandate — the buyer’s bank and the merchant can both trust that the agent was authorised to spend.
You serve: payment intent acceptance compatible with AP2 mandates.
Spec: https://cloud.google.com/blog/products/ai-machine-learning/announcing-agents-to-payments-ap2-protocol

MCP — Model Context Protocol

Backed by: Anthropic
What it does: A live server agents connect to (Claude, Cursor, Codex, Gemini CLI). The agent calls tools to read your catalogue and place orders in plain language — no scraping, no brittle integration.
You serve: an MCP server exposing catalogue + order tools.
Spec: https://modelcontextprotocol.io/

How they fit together

                    ┌─────────────────────────────┐
   Agent reads ───▶ │  UCP profile (.well-known)  │  "what do you support?"
                    └──────────────┬──────────────┘
                                   │ points at
              ┌────────────────────┼────────────────────┐
              ▼                    ▼                    ▼
        ACP checkout         MCP server           AP2 payment
        (discover + buy)     (talk to the store)  (signed authorisation)

UCP is the front door — it advertises ACP, MCP and AP2 support. An agent reads the UCP profile, then uses whichever transport fits: ACP or MCP to browse and order, AP2 to authorise payment.

What Mercentia serves

Every Mercentia store serves the full stack by default — no plugin, no paid add-on:

Protocol	Version published	Endpoint
UCP	2026-04-08	`/.well-known/ucp`
ACP	2026-04-17	`/.well-known/acp`
AP2	1.0	agent checkout intent
MCP	1.x	per-store MCP server

You can see the live conformance matrix on the agentic commerce hub, and check your own store’s status from Settings → Agentic commerce in the dashboard, which runs live pre-flight checks against each endpoint.