ucp-checkout-mcp

name	ucp-checkout-mcp
description	Implement UCP Checkout over the MCP (Model Context Protocol) binding — expose checkout operations as MCP tools for AI agents. Use when building an MCP server that AI agents like Claude or Gemini can call for commerce, or when integrating with Shopify's MCP endpoint.

UCP Checkout — MCP Binding

Before writing code

Fetch live spec: Web-search site:ucp.dev specification checkout-mcp and fetch the page for exact tool definitions, JSON-RPC envelope format, and _meta requirements.

For Shopify's production MCP server, fetch https://shopify.dev/docs/agents/checkout/mcp for auth flow and endpoint details.

Conceptual Architecture

How MCP Maps to UCP

UCP over MCP is a 1:1 mapping of checkout operations to MCP tools using JSON-RPC 2.0. The same data model as REST, different envelope.

Five MCP Tools

MCP Tool Name	Maps To	Key Inputs
create_checkout	POST /checkout-sessions	checkout object + idempotency_key
get_checkout	GET /checkout-sessions/{id}	id
update_checkout	PUT /checkout-sessions/{id}	id + checkout object
complete_checkout	POST .../complete	id + payment_data + idempotency_key
cancel_checkout	POST .../cancel	id + idempotency_key

Meta Requirements

Every MCP tool call MUST include _meta.ucp.profile pointing to the platform's UCP profile URI. This replaces the UCP-Agent HTTP header from the REST binding.

Error Mapping

UCP errors embed inside JSON-RPC 2.0 error responses:

• JSON-RPC error.code: -32603 (Internal Error)
• JSON-RPC error.data: Contains an errors[] array, where each error has code, message, severity, and details fields

When to Use MCP Binding

• You're building a merchant MCP server that AI agents (Claude, Gemini, etc.) call via tool use
• You're integrating with an existing MCP server (e.g., Shopify's)
• You want AI agents to autonomously browse and purchase without REST client code

Implementation Guidance

Building a Business MCP Server:

1. Implement the 5 tools using your MCP framework (e.g., @modelcontextprotocol/sdk for Node, mcp for Python)
2. Extract _meta.ucp.profile from every tool call for negotiation
3. Return checkout objects as JSON in the MCP tool result
4. Return errors using JSON-RPC error format with UCP data payload
5. Implement idempotency on create and complete tools

Connecting to an existing MCP server (e.g., Shopify):

1. Authenticate (Shopify uses OAuth2 client_credentials for access tokens)
2. Connect to the MCP endpoint
3. Call tools with proper _meta.ucp.profile and checkout payloads
4. Parse tool results for checkout status and messages

Shopify MCP Integration

Shopify provides a production MCP server for UCP checkout. Before implementing:

• Fetch https://shopify.dev/docs/agents/checkout/mcp for the latest auth flow, endpoint URL format, and error codes
• Authentication uses POST https://api.shopify.com/auth/access_token with client credentials
• MCP endpoint is POST https://{shop-domain}/api/ucp/mcp