UCP Example

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Minimal implementation of the Universal Commerce Protocol (UCP) — spec version v2026-04-08.

Built to understand UCP from the inside. Implements a merchant MCP server and an agent client that calls it via MCP tool calls.

What's here

  • src/server.ts — UCP merchant (TicketShop) as an MCP server, exposing 5 checkout tools
  • src/client.ts — AI agent that connects via MCP stdio and buys a ticket
  • src/types.ts — UCP types (CheckoutObject, Price, UCPMeta, etc.)
  • OBSERVATIONS.md — What we learned implementing this from scratch

Run it

npm install

# Run client (it spawns the server automatically via stdio)
npm run client

# Or run server standalone (connect via Claude Code or any MCP client)
npm run server

Connect via Claude Code

Add to your Claude Code MCP config:

{
  "mcpServers": {
    "ucp-ticketshop": {
      "command": "tsx",
      "args": ["/path/to/ucp-example/src/server.ts"]
    }
  }
}

Then ask Claude: "Buy me a TOKEN2049 VIP pass from TicketShop." Claude will call create_checkout, update_checkout, and complete_checkout as tool calls.

Key observations

See OBSERVATIONS.md for the full findings. The most important:

MCP as transport is the most interesting design decision. UCP is the only commerce protocol with a native MCP binding — an AI agent using Claude or any MCP client can check out via tool calls with zero adapter code. This is a meaningful advantage for LLM-native agent runtimes.

The cross-merchant budget gap persists. UCP has no Allowance equivalent. A credential token authorizes a checkout but doesn't enforce the agent's total budget across merchants. Neither ACP nor UCP solves this. Neither is designed to.

Protocol

UCP supports REST, MCP, and A2A transports with the same checkout logic. This implementation covers MCP (stdio).

Compare with acp-example for the REST transport version.