Tools Disappear in Claude When Importing Libraries Like pandas

[ahmadsyria]

I'm building an MCP server with simple tools that work perfectly with Claude. For example, a basic tool like say_hello runs fine and is recognized inside Claude.

However, as soon as I import an external library like pandas (even without using it in any tool), the following happens:

All tools disappear in Claude.

I get a Server disconnected message inside Claude.

Claude no longer recognizes any registered tools, including the simple ones

`from mcp.server.fastmcp import FastMCP
from typing import Optional, Union
import pandas as pd

mcp = FastMCP("DemoServer")

Simple tool

@mcp.tool()
def say_hello(name: str) -> str:
"""Say hello to someone

Args:
    name: The person's name to greet
"""
return f"Hello, {name}! Nice to meet you."

if name == "main":
mcp.run()

`

This issue happens even if pandas is only imported and not used.

Removing the pandas import line resolves the issue immediately.

Note: even with numpy same issue