You added an MCP server to Cursor and it will not connect — a red dot, "no tools available", or the server just is not there. Almost every case is one of nine causes. Work down the list in order.
1. Check the config file location
Cursor reads MCP servers from ~/.cursor/mcp.json (global) or .cursor/mcp.json in the project root (project-scoped). Editing the wrong one is the most common mistake. Full breakdown in MCP config file location.
2. Validate the JSON
A single trailing comma or missing brace makes Cursor silently ignore the whole file. Paste it into a JSON validator. The top-level key must be mcpServers.
3. Restart — fully
Cursor does not always hot-reload MCP config. Open Settings → MCP and toggle the server off/on, or quit and relaunch Cursor entirely.
4. Confirm Node is installed and recent
Most servers run via npx, which needs Node 18+. In a terminal run node --version. If it is missing or old, install from nodejs.org. If npx is not on Cursor's PATH, use an absolute path to node/npx in the config.
5. Test the server outside Cursor
Run the exact command from your config in a terminal, e.g. npx -y @modelcontextprotocol/server-filesystem /path. If it errors there, the problem is the server or its args, not Cursor.
6. Fix spawn npx ENOENT
This means Cursor cannot find npx. On macOS, GUI apps do not always inherit your shell PATH. Use the full path (which npx to find it) as the command, or launch Cursor from the terminal.
7. Mind the ~40-tool cap
Cursor limits how many tools it will load. Stack too many servers and later ones get dropped — "no tools available" for the overflow. Trim to four to six servers, or disable unused ones. Our curated loadouts are sized with this in mind.
8. Check the transport type
For remote servers, the entry needs the right shape ("url" for HTTP/SSE servers, command/args for stdio). Mixing them up yields a silent failure.
9. Read the MCP logs
Cursor surfaces MCP errors in the Output panel — select the MCP channel. The actual error message (bad token, missing scope, crashed process) is usually right there.
Still stuck?
If the server works in a terminal but not in Cursor, it is almost always PATH (#6) or the 40-tool cap (#7). On Claude Desktop instead? See Claude Desktop MCP not loading. Setting up from scratch? Start with the Cursor MCP setup guide.