Fast MCP Server Initializes Twice

[dino-su]

Describe the bug

When running Fast MCP Server with the current configuration, the server initializes twice in quick succession (within ~1 second). This can be observed in the logs where the "Initializing server..." message appears twice, followed by two successful connections and identical initialize method calls.

To Reproduce

1. Configure Fast MCP Server with the following settings:

"git": {
  "command": "uv",
  "args": [
    "run",
    "--with",
    "mcp[cli]",
    "mcp",
    "run",
    "fastmcp_git_servers.py"
  ]
}

2. Start the Claude Desktop app
3. Observe the duplicate initialization messages

Observation

The server initializes twice as shown in the logs below. Note the timestamps showing two initialization sequences less than 1 second apart:

2025-03-16T13:52:00.467Z [Git] [info] Initializing server...
2025-03-16T13:52:00.491Z [Git] [info] Server started and connected successfully
2025-03-16T13:52:00.495Z [Git] [info] Message from client: {"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0}
2025-03-16T13:52:01.398Z [Git] [info] Initializing server...
2025-03-16T13:52:01.707Z [Git] [info] Server started and connected successfully
2025-03-16T13:52:01.708Z [Git] [info] Message from client: {"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0}

Expected behavior
The server should initialize only once per execution.

Desktop (please complete the following information):

• OS: macOS Sonoma 14.2.1
• Claude Desktop: 0.8.1
• Python SDK: 1.4.0

Additional context

The non-fast MCP server implementation doesn't have this problem. The key difference appears to be in how the server is launched:

"git": {
  "command": "uv",
  "args": [
    "--directory",
    "src/non-fast-mcp-server",
    "run",
    "git"
  ]
}

[pavelanni]

I see the same behavior but with a different server written in Go. I guess it's a feature of Claude Desktop, not the FastMCP library.

I tested my server with the mcp-cli client (https://github.com/chrishayuk/mcp-cli), and it started my server only once.

I'm still investigating.

[osorionicolas]

same here with a server written in Spring AI