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/list requests
• 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

References

• FastMCP 2.14 Release Notes
• FastMCP Breaking Changes Policy