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Direct Execution

Inspector Tool

Currently testing of endpoints can be performed with the following command:

uv run mcp dev server.py

This will start a local server running Inspector than can be used to interact with the MCP tools.

inspector

Under the hood

You can run the server directly with the following command:

uv run mcp run server.py --transport sse

Note

This will start a local MCP server on port 8000.

Setting sse allows us to communicate with the server via HTTP using the Server-Sent Events protocol. This is a one-way communication channel from the server to the client. The client can send messages to the server using the POST method, but the server can only send messages to the client using the GET method.

We can establish an MCP client by making a request to the sse endpoint of the server:

curl http://0.0.0.0:8000/sse

This will return an output of the form:

event: endpoint
data: /messages/?session_id=<session_id>

and then ping incrementally.

As per the MCP docmentation, a client-server lifecycle consists of three stages: connection, exchange, and termination.

The lifecycle of an MCP connection involves three main stages:

Initialization:

  • The client sends an initialize request, including its protocol version and capabilities.
  • The server responds with its protocol version and capabilities.
  • The client sends an initialized notification to acknowledge.
  • Normal message exchange begins.

Message Exchange: After initialization, clients and servers can exchange messages using these patterns:

  • Request-Response: The client sends a request, and the server responds.
  • Notifications: Either side sends one-way messages (no response expected).

Termination: The connection can be terminated in several ways:

  • Clean shutdown via a close() method.
  • Transport disconnection.
  • Error conditions.

Initialisation Requests

  1. Send an initialisation request.
curl "http://0.0.0.0:8000/messages/?session_id=<session_id>" \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
  "method": "initialize",
  "params": {
    "protocolVersion": "2024-11-05",
    "capabilities": {
      "sampling": {},
      "roots": {
        "listChanged":true
        }
      },
      "clientInfo": {
        "name": "mcp-inspector",
        "version": "0.8.0"
        }
      },
      "jsonrpc":"2.0",
      "id":0
    }
}'
  1. Send an initialisation notification.
curl "http://0.0.0.0:8000/messages/?session_id=<session_id>" \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
        "method": "notifications/initialized",
        "jsonrpc": "2.0"
    }'

Now the server and client are initialised and ready to exchange messages.

Message Exchange

  1. We can now start to interact with the server. Typically, the client might start by listing the tools.
curl "http://0.0.0.0:8000/messages/?session_id=<session_id>" \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
        "method": "tools/list",
        "params": {},
        "jsonrpc": "2.0",
        "id": 1
    }'