MCP server disconnects immediately – transport closes after initialization (GoMarble and Filesystem extensions)

Title: MCP server disconnects immediately – transport closes after initialization (GoMarble and Filesystem extensions)

Body:

Hi team,

I’m experiencing repeated disconnection issues when trying to connect MCP extensions (e.g. GoMarble and Filesystem) in Claude Desktop. The server always starts and logs “connected successfully”, but then terminates shortly after receiving the initialize call from the client.

This happens consistently across different MCP servers, including GoMarble and Filesystem.

🖥️ System details:
OS: [e.g. Windows 11 x64]

Node.js version: [e.g. v20.11.1]

Claude Desktop version: Latest

Extensions tested: GoMarble MCP server, Filesystem server

📄 Behaviour:
Each time:

MCP server initialises correctly

Client sends:

json
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{"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0}
Server logs:

arduino
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Server transport closed unexpectedly, this is likely due to the process exiting early
Server disconnected.
🔁 What I’ve tried:
Fresh install of Claude Desktop

Reinstall Node.js

Manual testing of server (runs fine outside Claude)

Disabled antivirus + VPN

Tried different network

Used older and newer protocol versions

🧪 Example log (GoMarble MCP Server):
css
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[info] Server started and connected successfully
[info] Message from client: { ... }
[info] Server transport closed unexpectedly
[error] Server disconnected
Can you confirm if this is a known protocol issue, recent bug, or if I’m missing some config on the Claude side?

Thanks in advance!

Let me know your OS and Node.js version, and I’ll fill that in for you before you post it.

✅ 2. Test MCP call manually
Here’s how you can manually test the MCP server outside Claude:

🛠 Prerequisites:
Make sure Node.js is installed:
Run node -v in terminal to check

You have the MCP server code (e.g. GoMarble or Filesystem)

Install dependencies:

bash
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npm install
✅ Run the MCP server:
In terminal, navigate to the directory:

bash
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cd path/to/gomarble-mcp-server
node index.js
Or however your server starts.

You should see:

arduino
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Server started and connected successfully
✅ Send a manual JSON-RPC initialize call:
You can use curl, Postman, or a Node.js script. Here’s a curl example assuming it runs on localhost:3000 (adjust port if needed):

bash
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curl -X POST http://localhost:3000 \
-H "Content-Type: application/json" \
-d '{
"jsonrpc": "2.0",
"id": 0,
"method": "initialize",
"params": {
"protocolVersion": "2025-06-18",
"capabilities": {},
"clientInfo": {
"name": "claude-ai",
"version": "0.1.0"
}
}
}'