MCP Config Fixer for Windows

MCP server won't connect? Getting spawn npx ENOENT, or the tools just won't show up? Paste your claude_desktop_config.json below — this validates the JSON, finds the Windows problems, and outputs a corrected, Windows-safe config. 100% in your browser; nothing is uploaded.

Why MCP servers fail on Windows

On Windows, npx and uvx are .cmd shims. The low-level process spawn that Claude Desktop / Claude Code / Cursor / Cline use to launch a stdio server cannot execute a .cmd file directly (it doesn't go through the shell that resolves PATHEXT). So a bare "command": "npx" fails with spawn npx ENOENT — even though npx works fine in your terminal. The fix is to wrap it so Windows' command interpreter resolves the shim:

// Fails on Windows
{ "command": "npx", "args": ["-y", "@some/mcp-server"] }

// Works on Windows
{ "command": "cmd", "args": ["/c", "npx", "-y", "@some/mcp-server"] }

This tool applies that transform automatically, plus checks for the other silent killers: invalid JSON (a single trailing comma disables every server), a missing mcpServers key, unescaped \ in Windows paths, relative paths that should be absolute, and env blocks placed in the wrong spot.

Related guides

• The most common claude_desktop_config.json mistakes
• MCP server not showing up? How to debug it
• How to add an MCP server to Claude Desktop

FAQ

I get spawn npx ENOENT but npx works in my terminal. Why?

Claude Desktop spawns the server without a shell, so it can't resolve the npx.cmd shim. Wrap the command in cmd /c (this tool does it for you).

Why did ALL my servers disappear after one edit?

A single JSON syntax error (often a trailing comma) invalidates the whole file, so the client loads zero servers. Paste it here to find the exact problem.

Does this upload my config?

No. Everything runs locally in your browser — your tokens never leave your machine.

Free tool by Hatchloop · CLI version: pip install mcp-config-lint · MCP Setup Pack · All guides