MCPServer.add_tool() missing execution parameter for task support declaration (spec compliance gap) #2156

Description

The MCP spec (2025-11-25) requires tools to declare task support via execution.taskSupport in the tools/list response:

In the result of tools/list, tools declare support for tasks via execution.taskSupport, which if present can have a value of "required", "optional", or "forbidden".

While server.experimental.enable_tasks() correctly handles server-level capabilities and task handler registration, there is no way to set execution.taskSupport on individual tools through the high-level API.

Current behavior

MCPServer.add_tool() (and the internal Tool model in mcp/server/mcpserver/tools/base.py) does not accept an execution parameter. Tools registered via add_tool() will always have execution: null in the tools/list response, which per spec means taskSupport defaults to "forbidden".

This means even when enable_tasks() is called and the server declares tasks.requests.tools.call capability, clients like the MCP Inspector see taskSupport as "forbidden" and disable the "Run as task" option.

Expected behavior

MCPServer.add_tool() should accept an optional execution parameter (of type ToolExecution) so developers can declare taskSupport per tool:

from mcp.types import ToolExecution, TASK_OPTIONAL

mcp.add_tool(
    my_handler,
    name="long_running_tool",
    description="A tool that takes a while",
    execution=ToolExecution(taskSupport=TASK_OPTIONAL),
)

Workaround

Currently the only workaround is to monkey-patch the tools/list handler to inject execution.taskSupport into the response:

server = mcp._lowlevel_server
original = server._request_handlers.get("tools/list")

async def patched(ctx, params):
    result = await original(ctx, params)
    for tool in result.tools:
        tool.execution = ToolExecution(taskSupport=TASK_OPTIONAL)
    return result

server._request_handlers["tools/list"] = patched

Affected files

• src/mcp/server/mcpserver/tools/base.py — Tool model and Tool.from_function() missing execution field
• src/mcp/server/mcpserver/tools/tool_manager.py — ToolManager.add_tool() missing execution parameter
• src/mcp/server/mcpserver/server.py — MCPServer.add_tool() missing execution parameter

References

• MCP Spec 2025-11-25 — Tasks: Tool-Level Negotiation
• SEP-1686 Tasks implementation PR #1645
• SEP-1686 tracking issue #1546