MCP Transport

AgentCart exposes a Model Context Protocol endpoint for AI agents that use JSON-RPC 2.0 instead of REST.

Endpoint


POST https://app.agentcart.io/api/ucp/{slug}/mcp
Content-Type: application/json

Protocol

Standard JSON-RPC 2.0. Every request has:


{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/list",
  "params": {}
}

Discovering tools


curl -X POST https://app.agentcart.io/api/ucp/{slug}/mcp \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}'

Returns the four available tools: create_checkout_session, get_checkout_session, complete_checkout_session, cancel_checkout_session.

Calling a tool


{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "tools/call",
  "params": {
    "name": "create_checkout_session",
    "arguments": {
      "line_items": [
        { "item": { "id": "gid://shopify/Product/123456" }, "quantity": 1 }
      ]
    }
  }
}

The response wraps the REST API response in MCP content format:


{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "content": [
      { "type": "text", "text": "{\"id\":\"...\",\"status\":\"requires_escalation\",...}" }
    ]
  }
}

Error codes

Code	Meaning
`-32700`	Parse error — invalid JSON
`-32601`	Method or tool not found
`-32602`	Missing required parameter
`-32000`	Upstream error from REST endpoint

CORS

The MCP endpoint allows cross-origin requests from any origin. No API key is required beyond the merchant’s slug being in the URL.