Where does the bug appear (feature/product)?
Cursor IDE
Describe the Bug
When an MCP server exposes tools with dots in their names (e.g. sdl.symbol.search, sdl.repo.status), Cursor displays a warning in the MCP settings panel stating “Tool name must only contain alphanumeric characters and underscores” and implies the tools will be filtered out.
However, the tools are successfully invoked by the agent and return correct results despite the warning. The warning is misleading — it suggests the tools are non-functional when they are not.
Steps to Reproduce
Install SDL-MCP: npm install -g sdl-mcp
Configure it as an MCP server in ~/.cursor/mcp.json
Start Cursor
Open Cursor Settings > MCP
Observe yellow warning panel listing all sdl.* tools as having naming issues (“Tool name must only contain alphanumeric characters and underscores”)
Open Cursor Agent chat
Run: “Using SDL tools, find all the places in this codebase where a new user session is created and stored in the database”
Observe Ran Sdl.Symbol.Search, Ran Sdl.Repo.Status, Ran Sdl.Symbol.Get Card appearing in agent tool call blocks
Observe correct, detailed results returned from the tools
Expected: Warning should not appear if tools are callable, or tools should actually be filtered if the naming is invalid
Actual: Warning appears saying tools will be filtered, but tools execute successfully — false positive
Expected Behavior
The warning should accurately reflect reality. Either:
If dot-separated tool names are truly invalid, filter them out and warn that they are unavailable, OR
If dot-separated tool names are acceptable and tools will work, show no warning
The current state — displaying a warning that tools “may be filtered out” while simultaneously calling them successfully — is contradictory and creates unnecessary confusion for users trying to diagnose MCP connectivity issues.
Operating System
MacOS
Version Information
Environment details:
VS Code Extension API: 1.105.1
Commit: 80c653c2c3528e65016a0d304b54486084b470b0
Date: 2026-06-07T01:42:56.126Z (1 day ago)
Layout: editor
Build Type: Stable
Release Track: Default
Electron: 39.8.1
Chromium: 142.0.7444.265
Node.js: 22.22.1
V8: 14.2.231.22-electron.0
xterm.js: 6.1.0-beta.256
OS: Darwin arm64 25.5.0
For AI issues: which model did you use?
Sonnet 6
Additional Information
This is more confusing than anything else. Cursor is explicitly telling me these MCP tools will not work, but they actually do. Its a false positive warning that fires when there’s no real problem, degrading the user experience.
Does this stop you from using Cursor
No - Cursor works, but with this issue