MCP, A2A and Google UCP do different jobs. MCP connects an AI application to a store's tools and data, A2A lets one AI agent work with another agent, and UCP is an open commerce standard that Google uses for buying in AI Mode and Gemini. StartShop.ai exposes all three from one Shopify, WooCommerce or StartShop Native store.
What is the difference between A2A, MCP and Google UCP for commerce?
Each answers a different question an AI agent has before it buys:
- What can I call? MCP: how an AI application uses tools and data.
- Who do I work with? A2A: how one agent hands a task to another.
- How do I check out? UCP: a commerce standard for catalog, cart, checkout and orders.
They are not rivals. The A2A project calls MCP and A2A "highly complementary", and ucp.dev lists A2A, MCP and AP2 support as built into UCP.
MCP: how an AI application uses your store's tools
Anthropic open-sourced the Model Context Protocol in November 2024 as a standard for connecting AI assistants to the systems where data lives. The specification describes hosts (AI applications), clients and servers exchanging JSON-RPC 2.0 messages. Servers offer resources, prompts and tools, and tools are "functions for the AI model to execute". The MCP documentation names Claude and ChatGPT among the AI applications that can connect to MCP servers.
In a store, your commerce system is the server and the assistant calls tools such as "search the catalog" or "start a checkout". MCP itself is general-purpose: the specification talks about tools, resources and prompts, not products or orders.
A2A: how one agent works with another agent
Google announced the Agent2Agent protocol (A2A) on 9 April 2025 as an open protocol that lets AI agents communicate, exchange information securely and coordinate actions. The A2A site says it was later donated to the Linux Foundation. The specification lets agents discover each other's capabilities, manage shared tasks and exchange information without seeing each other's internal state, memory or tools.
The A2A site puts it plainly: MCP is agent-to-tool, A2A is agent-to-agent. In commerce, a shopper's agent can hand a store's shopping agent a task, such as "find a wool jacket that arrives by Friday", and get the result back.
Google UCP: the commerce standard behind buying in Google's AI surfaces
The Universal Commerce Protocol (UCP) calls itself "the common language for platforms, agents, and businesses". It is an open standard covering catalog search and lookup, cart building, identity linking, checkout and order management, over REST and JSON-RPC. ucp.dev lists Google among several companies that co-developed it, so it is not a Google-only format.
Google's merchant page explains the "Google" in Google UCP: adopting UCP enables direct buying in AI Mode in Google Search and Gemini. The merchant stays the Merchant of Record and uses existing Merchant Center feeds. Google also runs a waitlist, so exposing a UCP checkout and being live on Google's AI surfaces are separate steps.
A2A, MCP and UCP side by side
| Protocol | Who calls it | What it is used for in a store | What StartShop.ai exposes |
|---|---|---|---|
| MCP | An AI application, such as an assistant, acting as an MCP client | Calling the store's tools: search, quotes, checkout | An MCP surface, with the same scoped API keys as its REST interface |
| A2A | Another AI agent | Agent-to-agent tasks: discover the store's agent, hand it a task, get the result | An A2A surface for AI agents |
| Google UCP | Platforms and agents that implement UCP; on Google, AI Mode in Google Search and Gemini | Catalog, cart, checkout and orders in one commerce standard | UCP checkout sessions |
Where payments fit: ACP and AP2
Payment has its own standards. ucp.dev names the Agent Payments Protocol (AP2) for secure payment through payment mandates and verifiable credentials, and AP2 describes itself as available as an extension for A2A and UCP. The Agentic Commerce Protocol (ACP) is an open standard for programmatic commerce flows; its site names ChatGPT as the first AI platform to implement it and Stripe as the first compatible payment provider.
With StartShop.ai, checkout stays on the payment rails you already run. For what each specifies, read ACP vs. AP2: The 2026 Standards Guide.
What a merchant needs to do
You don't implement three protocols yourself. With StartShop.ai:
- Connect your store. Shopify or WooCommerce, or StartShop Native if you have no commerce backend. Inventory, pricing and fulfilment stay in your platform.
- Open the agent surfaces. Turn on A2A and MCP for agents. Agent builders request access through the developer portal, and you approve.
- Set the controls. Every API key has explicit scopes (search, quote, negotiate, checkout, order) and a per-minute rate limit you set. Every call is audited, and you can revoke a key in one click.
- Pick a plan when it makes sense. StartShop.ai has four plans: Free $0 per month, Growth $99 per month, Pro $499 per month and Enterprise with custom pricing. See How much does an agentic commerce platform cost?
Still deciding whether agents should buy from you at all? Read Can AI shopping agents buy from my WooCommerce or Shopify store? or What is agentic commerce? Agent builders: see the developer page.
FAQ
What is the difference between A2A, MCP and Google UCP for commerce?
MCP connects an AI application to a store's tools, A2A connects one agent to another, and UCP is an open commerce standard for catalog, cart, checkout and orders that Google uses in AI Mode and Gemini.
Do I need MCP, A2A or UCP for my store?
You need the ones your target agents speak, and they work together. StartShop.ai exposes A2A, MCP and Google UCP surfaces from one connected store, so you don't have to pick.
Is Google UCP only for Google Shopping?
No. UCP is an open standard at ucp.dev, co-developed by several companies. On Google, it enables direct buying in AI Mode in Google Search and Gemini, and Google runs a waitlist for merchants.
Can my Shopify or WooCommerce store support all three?
Yes. StartShop.ai connects to Shopify or WooCommerce, or you can use StartShop Native, and AI agents can then use its A2A, MCP and Google UCP surfaces.
Where do payments (ACP / AP2) fit in?
They cover the payment step: AP2 works as an extension for A2A and UCP, and ACP is an open standard for programmatic commerce flows. With StartShop.ai, checkout stays on your existing payment rails.
Do I need a developer?
You connect an existing Shopify or WooCommerce store, or start with StartShop Native if you have no commerce backend. Teams that want their own integration use the REST and MCP surface on the developer page.
Start on the Free plan
Connect your store and open it to shoppers and AI agents before you pay.