MCP servers fail on Windows with npx (use cmd /c)

The error

Why it happens

On Windows, npx is a npx.cmd batch script, which cannot be spawned directly without a shell. Clients that spawn the command directly fail.

How to fix it

1. Wrap npx with cmd /c
   Make cmd the command and pass /c npx … as args.

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

2. Escape backslashes
   In JSON every Windows path backslash must be doubled: C:\\Users\\you.
3. Add APPDATA if npm cannot find its cache
   Some setups need APPDATA passed through.

   "env": { "APPDATA": "C:\\Users\\you\\AppData\\Roaming\\" }

Related servers

Sources

• https://modelcontextprotocol.io/docs/develop/connect-local-servers
• https://nodejs.org/api/child_process.html#spawning-bat-and-cmd-files-on-windows
• MCP servers cannot start: npx.cmd missing (Windows) (GitHub issue, 1 comments)
• Windows: stdio MCP servers fail with "spawn npx ENOENT" (v2 engine regression) (GitHub issue, 2 comments)
• MCP server spawn fails on Windows for .cmd executables (npx, etc.) (GitHub issue, 3 comments)