MCP server fails to start in Claude Desktop: 'spawn npx ENOENT' (or 'spawn uvx ENOENT', 'Server disconnected'). How do I fix it?

Cause: ENOENT means the program in the server's "command" couldn't be found. Claude Desktop and other GUI apps don't start with your terminal's PATH, so npx, node, uvx or python that work in a terminal may be invisible to them. This is especially common with nvm, fnm, asdf, Homebrew on Apple Silicon (/opt/homebrew/bin) and uv installed in ~/.local/bin. On Windows there is a second cause: npx is a .cmd batch file, which can't be launched directly as a process. How to check: - Open the MCP logs: on macOS ~/Library/Logs/Claude/mcp*.log, on Windows %APPDATA%\Claude\logs. The log shows the exact command that failed. - In a terminal, find the real path: which npx / which uvx (macOS/Linux) or where npx (Windows). Fix: 1. macOS/Linux: put the absolute path in claude_desktop_config.json, for example "command": "/opt/homebrew/bin/npx" or the path printed by which uvx. If you use nvm, use the path of a specific Node version, or add an "env" entry with a PATH that includes that Node's bin directory, since npx itself launches node. 2. Windows: run it through cmd: "command": "cmd", "args": ["/c", "npx", "-y", "<package>", ...]. Alternatively point "command" at node.exe and pass the server's script path in args. 3. Fully quit Claude Desktop (not just close the window) and start it again, since the config is read only at startup. After: the server should show as connected with its tools listed. If it now starts but disconnects, read the same log: that is usually a missing environment variable (API keys must go in the server's "env" block, not your shell profile) or the server writing non-protocol output to stdout. Sources: https://modelcontextprotocol.io/legacy/tools/debugging https://docs.getdbt.com/faqs/dbt-mcp/troubleshooting/mcp-troubleshoot-claude-desktop-errors https://github.com/orgs/modelcontextprotocol/discussions/20