outputSchema is None

[yuhp-zts]

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

In the tool definition, outputSchema is included, but when calling the tools/list interface, the returned information shows outputSchema=None. What is the reason for this?

1. The content in the Tool information is:
   {'add_two_numbers': Tool(fn=<function add_two_number at 0x7f95ed506840>, name='add_two_numbers', title=None, description='', parameters={'properties': {'a': {'title': 'A', 'type': 'integer'}, 'b': {'title': 'B', 'type': 'integer'}}, 'required': ['a', 'b'], 'title': 'add_two_numberArguments', 'type': 'object'}, fn_metadata=FuncMetadata(arg_model=<class 'mcp.server.fastmcp.utilities.func_metadata.add_two_numberArguments'>, output_schema={'properties': {'result': {'title': 'Result', 'type': 'integer'}}, 'required': ['result'], 'title': 'add_two_numberOutput', 'type': 'object'}, output_model=<class 'mcp.server.fastmcp.utilities.func_metadata.add_two_numberOutput'>, wrap_output=True), is_async=False, context_kwarg=None, annotations=None)}

2. The result of calling tools/list is:
   Tool(name='add_two_numbers', title=None, description='', inputSchema={'properties': {'a': {'title': 'A', 'type': 'integer'}, 'b': {'title': 'B', 'type': 'integer'}}, 'required': ['a', 'b'], 'title': 'add_two_numberArguments', 'type': 'object'}, outputSchema=None, annotations=None, meta=None)

Is it because ToolInfo does not include this information?

Example Code

Python & MCP Python SDK

import requests
import asyncio
from mcp import ClientSession
from mcp.client.streamable_http import streamablehttp_client
from mcp.client.sse import sse_client
from mcp.client.stdio import stdio_client
from mcp.server import FastMCP

async def main():
    url = "http://localhost:9200/mcp" 
    async with streamablehttp_client(url=url) as (read, write,id):
        async with ClientSession(read, write) as session:
            await session.initialize()
            tools_list = await session.list_tools()
……