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Pin FastMCP to 2.12.3 - Version 2.14.x breaks MCP tools visibility #463
Description
Problem
Users report that MCP tools are not visible in Claude Desktop after FastMCP was upgraded to 2.14.x in production. The tools are registered correctly server-side but clients cannot see them.
Root Cause
Our dependency constraint fastmcp>=2.10.2 allowed production to upgrade to FastMCP 2.14.1 + MCP SDK 1.24.0, while our lockfile had 2.12.3 + 1.14.0.
FastMCP 2.14.0 includes breaking changes:
- Tool name validation at registration time (SEP-986)
- Removed deprecated APIs (BearerAuthProvider, Context.get_http_request(), dependencies parameter)
- Mount/import argument changes
Evidence
- Production shows 17 tools registered correctly
- MCP endpoint responds and handles
tools/listrequests - But Claude Desktop users report tools not visible
- User confirmed pinning to 2.12.3 fixes the issue
User Report
Discord conversation confirming fix: https://discord.com/channels/1368009106061000777/1381294195553341531/1451703784165343426
Solution
Pin FastMCP to 2.12.3 until we can properly test and migrate to 2.14.x.
Version Comparison
| Package | Lockfile (working) | Production (broken) |
|---|---|---|
| fastmcp | 2.12.3 | 2.14.1 |
| mcp | 1.14.0 | 1.24.0 |
Activity
claude commentedon Dec 20, 2025
Claude finished @groksrc's task in 1m 54s —— View job •
claude/issue-463-20251220-0115• Create PR ➔Issue analyzed and fix implemented ✓
Issue Triage:
Analysis:
This is a critical bug where FastMCP 2.14.x introduced breaking changes that prevent Claude Desktop from seeing MCP tools, despite them being registered correctly server-side. The issue has been confirmed by users, with pinning to 2.12.3 resolving the problem.
Changes Made:
Implementation:
Changed
pyproject.tomlline 32 from:to:
This pins FastMCP to the last known working version (2.12.3) until the team can properly test and migrate to 2.14.x with its breaking changes.
Next Steps:
The lockfile (
uv.lock) will need to be updated by runninguv synclocally. The CI/CD pipeline should handle this automatically when the PR is merged.| Branch: claude/issue-463-20251220-0115
fix: Pin FastMCP to 2.12.3 to restore MCP tools visibility
fix: Pin FastMCP to 2.12.3 to fix MCP tools visibility
feat: upgrade fastmcp 2.12.3 to 3.0.1 with tool annotations