Fix "spawn npx ENOENT" in MCP Server Setup

Why This Happens

MCP clients launch your server as a subprocess. When the config says "command": "npx", the client calls the operating system to find and run npx. The error means the OS could not find it. Three common causes:

1. Windows: npx is a .cmd script, not a binary executable. Some MCP clients cannot run .cmd files directly.
2. nvm / mise / Homebrew: Node.js installed via a version manager is not in the system PATH that GUI applications inherit. Your terminal finds npx, but Claude Desktop does not.
3. Node.js not installed: npx comes with Node.js. If Node is not installed, npx does not exist.

Fix 1: Windows — Use cmd /c Wrapper

On Windows, wrap the command with cmd /c:

{
  "mcpServers": {
    "my-server": {
      "command": "cmd",
      "args": ["/c", "npx", "-y", "@modelcontextprotocol/server-filesystem", "C:\Users\you\docs"]
    }
  }
}

This tells Windows to run npx through the command processor, which knows how to handle .cmd scripts.

Fix 2: Use Absolute Path to npx

Find the full path to npx and use it directly:

# macOS / Linux
which npx
# Example output: /usr/local/bin/npx

# Windows
where npx
# Example output: C:\Program Files\nodejs\npx.cmd

Then use the absolute path in your config:

{
  "mcpServers": {
    "my-server": {
      "command": "/usr/local/bin/npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/path/to/dir"]
    }
  }
}

Fix 3: nvm Users — Set the Correct Path

If you use nvm, the path to npx changes per Node version. Find it:

# macOS/Linux with nvm
nvm which current
# Example: /Users/you/.nvm/versions/node/v20.11.0/bin/node

# The npx path is in the same directory:
# /Users/you/.nvm/versions/node/v20.11.0/bin/npx

Use this full path in your MCP config. Note: if you switch Node versions with nvm use, you need to update the path.

For nvm-windows, the path is typically C:\Users\you\AppData\Roaming\nvm\v20.11.0\npx.cmd — and you still need the cmd /c wrapper.

Fix 4: Use uvx Instead of npx (Python MCP Servers)

For Python-based MCP servers, use uvx instead of npx:

{
  "mcpServers": {
    "my-python-server": {
      "command": "uvx",
      "args": ["my-mcp-server"]
    }
  }
}

uvx (from the uv package manager) does not have the .cmd issue on Windows.

Quick Diagnostic

Use our MCP Config Debugger — paste your config and it will automatically detect this error and suggest the fix for your OS.

Still Not Working?

• Make sure -y is the first argument after npx (skips the interactive confirmation prompt)
• Restart your MCP client after editing the config file
• On Windows, check if your config is at the correct path — see our Config Debugger for MSIX path issues
• Check the MCP client logs for more details (Claude Desktop: ~/Library/Logs/Claude/mcp*.log on macOS)