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UCP via MCP

The same operations as JSON-RPC tools, with the spec's tool names.

Endpoint/api/ucp/mcpTransportStreamable HTTPSpec version2026-04-08

MCP binding

The same operations as JSON-RPC tools, with the spec's tool names.

create_checkout
Start a checkout for one item, with an optional buyer and codes.
get_checkout
Read a checkout session by id.
update_checkout
Patch and re-price a checkout session.
complete_checkout
Charge and fulfil. Safe to retry.
cancel_checkout
Abandon an unfinished checkout.
tools/list
curl -X POST \
  https://go.sessions.website/@<handle>/api/ucp/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

The envelope

UCP-Agent and Idempotency-Key travel in the meta argument rather than in headers, matching the spec's MCP binding.

Every result carries structuredContent — the checkout object you parse — alongside a text rendering for clients that only read text.

Business outcomes are successes
A sold-out session or a declined card comes back as a normal result whose structuredContent.messages explains what happened — not as isError. isError is reserved for protocol failures like an unknown session id.
tools/call
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "create_checkout",
    "arguments": {
      "meta": {
        "ucp-agent": "https://you.example/ucp.json",
        "idempotency-key": "6f1e…"
      },
      "checkout": {
        "line_items": [
          {"item": {"id": "gid://Sessions/Pass/01J…"},
           "quantity": 1}
        ],
        "buyer": {"email": "ada@example.com"},
        "com.sessions.codes": {"discount": "SPRING20"}
      }
    }
  }
}

Paying

When the total is above zero, complete needs a credential in payment.instruments[]. Mark the instrument you want charged with selected: true; with a single instrument that is implied.

The token is a Stripe payment-method id created against the connected account the manifest advertises — initialise Stripe with the manifest's publishable_key and stripe_account, tokenize there, and send the resulting id. Sessions confirms it server-side on that same account.

Free checkouts need no credential
A zero-total checkout — a free class, a fully gift-card-covered purchase — completes with an empty body.

Pairing with discovery

This server is checkout only. It has no browse or search tools, because the public MCP server already has them and the ids line up.

An assistant can find a session there and hand the id straight to create_checkout here. Public MCP server

Next

UCP overviewUCP via RESTRead the MCP binding spec