I upgraded to FastMCP 3.2.3:
Name: fastmcp
Version: 3.2.3
Summary: The fast, Pythonic way to build MCP servers and clients.
Home-page: https://gofastmcp.com
Author: Jeremiah Lowin
Author-email:
License-Expression: Apache-2.0
Location: d:\work\code.tallyai.backend.venv\Lib\site-packages
Requires: authlib, cyclopts, exceptiongroup, httpx, jsonref, jsonschema-path, mcp, openapi-pydantic, opentelemetry-api, packaging, platformdirs, py-key-value-aio, pydantic, pyperclip, python-dotenv, pyyaml, rich, uncalled-for, uvicorn, watchfiles, websockets
Required-by:
(.venv) PS D:\work\code.tallyai.backen
Still no luck.
AI response:
Tool response: [{‘type’: ‘text’, ‘text’: ‘{\n “transport”: null,\n “companies”: [\n “Acme Corp”,\n “Globex Inc”,\n “Initech Ltd”\n ],\n “note”: “Fetched via None transport”\n}’, ‘id’: ‘lc_0541a012-cd29-4337-acb8-bad716058f2e’}]
AI response: Here are your companies: Acme Corp, Globex Inc, Initech Ltd.
Another difference, I am using ChatGoogleGenerativeAI(vertexai=True, …) , not ChatOpenAI.
I am using Gemini 2.5 Flash via Vertex AI. Could that be the issue?
I am using Windows OS for testing - can this be cause of the issue?
UPDATE:
Found the problem - it is Windows OS issue. Same code working fine in my Mac. With Mac the output coming correctly. But with Windows , it is not working. In Windows I am not even getting the info log when mc server starts in stdio mode “ [04/09/26 20:59:36] INFO Starting MCP server ‘tally-mcp-server’ with transport ‘stdio’“
Is FastMCP not supported in Windows?