**Memory Leak** in MCP Server – will be a memory leak until OOM (Out of Memory) occurs

[MadanMaram]

Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

As part of our usage of FastMCP and Python MCP SDK, we observed a memory leak in the MCP server. When the client continuously calls a simple tool (e.g., a greet function), the server's memory usage steadily increases over time and does not get released, eventually leading to an Out of Memory (OOM) condition.

This issue is reproducible both in the fastmcp library and the MCP SDK.

Issue

Here is the Logs:Memory will keep increasing
memory_log_pythonmcp.txt

Example Code

Server.py
----------------------------------------------------
from mcp.server.fastmcp import FastMCP

# Create an MCP server
mcp = FastMCP("Demo Server")

# Add a simple tool
@mcp.tool()
def greet(name: str) -> str:
 """Return a greeting message."""
 return f"Hello, {name}!"

if __name__ == "__main__":
 # Run the server with streamable HTTP transport
 mcp.run(transport="streamable-http")

--------------------------------------------------
client.py(（with a while loop）
---------------------------------------------------
import asyncio
from mcp.client.streamable_http import streamablehttp_client
from mcp.client.session import ClientSession

async def call_tool(name: str):
 # Connect to the MCP server using streamable HTTP
 async with streamablehttp_client("http://127.0.0.1:8000/mcp") as (read, write, _):
 async with ClientSession(read, write) as session:
 # Initialize the connection
 await session.initialize()
 # Call the 'greet' tool
 result = await session.call_tool("greet", {"name": name})
 print(result)

async def main():
 while True:
 await call_tool("Bob")

if __name__ == "__main__":
 asyncio.run(main())
--------------------------------------------

Python & MCP Python SDK

Environment:

Python: 3.12.1

MCP Python SDK: 1.10.1

[Kludex]

Your text file doesn't show a leak, it just shows the memory increased.

Closing this issue, since I couldn't visualize the leak with memray.