UCP MCP server answers tools/list

What we check

When your profile declares an MCP transport under dev.ucp.shopping, we send that endpoint one MCP tools/list request, the call a client makes to see which tools a server offers. We compare the tool names it lists with the ones the UCP spec defines for the capabilities you declare: create_checkout, get_checkout, update_checkout, complete_checkout and cancel_checkout for checkout, the cart tools for cart, search_catalog, lookup_catalog and get_product for the catalog, and get_order for orders.

Why it matters

UCP maps each capability to MCP tools, so an agent using the MCP transport can only do what the server lists. A declared endpoint that does not answer as MCP, or that lists none of the tools for checkout, leaves an agent with nothing to call.

How we check

We send at most one request per scan, and only to the endpoint your own profile declares, over HTTPS to a public address. It is a stateless MCP 2026-07-28 tools/list, which lists tools and calls none of them. We follow no redirect, wait at most 5 seconds and read at most 1 MiB of the answer. PASS: every expected tool is listed. WARN: some are missing (scored by the share listed, never below 40), or the server answers with a JSON-RPC error (score 50). FAIL: the endpoint answers 404 or 410, or with something that is not JSON-RPC. SKIPPED: no MCP transport is declared, the endpoint is one our rules will not call, or it gave no answer we can grade.

How to fix it

1. Make the MCP endpoint in /.well-known/ucp answer a stateless MCP 2026-07-28 tools/list request.
2. List the UCP tools for each capability you declare.

What good looks like

"services": {
  "dev.ucp.shopping": [{
    "version": "2026-08-25",
    "transport": "mcp",
    "endpoint": "https://shop.example/api/ucp/mcp"
  }]
}

tools/list -> create_checkout, get_checkout, update_checkout, complete_checkout, cancel_checkout, ...

Sources

• UCP 2026-08-25 shopping service over MCP (mcp.openrpc.json)
• UCP 2026-08-25 checkout over MCP
• MCP 2026-07-28: tools

Read more

• UCP explained

  The Universal Commerce Protocol: the profile a store publishes at /.well-known/ucp, the capabilities it declares there, and the checkout flow from a new basket to a placed order.

• MCP, A2A and WebMCP for stores

  MCP, A2A and WebMCP: what each specification defines, what it could mean for a store that wants to offer tools to agents, and what status each gives itself.