MCP: one plug for every tool
The standard way agents find and call tools, message by message.
Every app used to wire up tools its own way. MCP, the Model Context Protocol, is the standard plug: write a tool server once, and Claude, ChatGPT, Cursor, VS Code and your own agents can all use it.
Underneath, it's JSON-RPC: small JSON messages over a pipe (stdio) or HTTP. Here is a real session, every message both ways.
- Client (agent)MCP server
1 of 13 · client → server
The client introduces itself and the protocol version it speaks.
{
"jsonrpc": "2.0",
"id": 1,
"method": "initialize",
"params": {
"protocolVersion": "2025-11-25",
"capabilities": {},
"clientInfo": {
"name": "glass-box-recorder",
"version": "1.0"
}
}
}Recorded from a real MCP server (Python SDK v2) over stdio, 2026-10-21
Which message gives the model its tools?