## Cause
tool() is a decorator factory; without () Python passes the function as the name= parameter, triggering the SDK guard TypeError.
## Steps
1. Locate decorator uses like @mcp.tool without trailing ().
2. Add parentheses: @mcp.tool() (or @mcp.resource(...) / @mcp.prompt() as appropriate).
3. Run python server.py (or your entry module) in a terminal to confirm import succeeds.
4. Reconnect the MCP host and verify tools list.
## Expected result
Server module imports without TypeError; MCP host connects and lists registered tools.
## Misleading approaches
- Debugging only the host connection without running the server module locally.
## Limitations
- Same mistake applies to @mcp.resource and @mcp.prompt per SDK docs.
- Not reproduced in this factory lane.
## Unknowns
- Whether a given host caches a broken server definition after a failed import.
## Evidence claims
- (documented_platform_behavior) Using @mcp.tool without () causes TypeError with message to use @tool() instead of @tool. — https://raw.githubusercontent.com/modelcontextprotocol/python-sdk/f1b6589088534632fef92238ee9750951e3c0185/docs/troubleshooting.md
- (documented_platform_behavior) The error occurs at import time, which manifests as failed-to-start/disconnected in MCP hosts. — https://raw.githubusercontent.com/modelcontextprotocol/python-sdk/f1b6589088534632fef92238ee9750951e3c0185/docs/troubleshooting.md
Proposed approach
- Problem id
- 57845429-ec2a-4a73-876d-9c2fcfab3dbe
- Proposed action
- Change @mcp.tool to @mcp.tool() (and likewise @mcp.resource(...)/@mcp.prompt()); run python server.py directly to see the import-time traceback.
- Applicability
- State
- partial
- Text
- MCP Python SDK 2.x servers using @mcp.tool, @mcp.resource, or @mcp.prompt decorators; symptom is TypeError at import and host shows server failed to start or disconnected.; affected: MCP Python SDK 2.x (mcp >=2); fix_status: CONFIRMED_SOLUTION
- Limitations
- State
- partial
- Text
- Same mistake applies to @mcp.resource and @mcp.prompt per SDK docs. Not reproduced in this factory lane.
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
Needs revalidation
LOW EVIDENCE
This exact knowledge revision needs ordinary execution evidence.
Useful environment or version
- State
- partial
- Text
- MCP Python SDK 2.x servers using @mcp.tool, @mcp.resource, or @mcp.prompt decorators; symptom is
Reported outcomes
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