MCP Config: Windows Path Handling

JSON + Windows Paths = Backslash Soup

JSON requires literal backslashes to be doubled (\\). Windows paths are full of backslashes. The combination is a famous source of "why won't this server start?" headaches.

Escaping correctly

Wrong (single backslash):

"args": ["-y", "@modelcontextprotocol/server-filesystem", "C:\Users\me\Documents"]

This produces invalid JSON.

Right (escaped backslash):

"args": ["-y", "@modelcontextprotocol/server-filesystem", "C:\\Users\\me\\Documents"]

Even better — use forward slashes, which Node and Python both handle on Windows:

"args": ["-y", "@modelcontextprotocol/server-filesystem", "C:/Users/me/Documents"]

Where to save the config on Windows

Claude Desktop expects:

%APPDATA%\Claude\claude_desktop_config.json

The shell variable %APPDATA% resolves to C:\Users\<you>\AppData\Roaming for most installs. Note this is the save path, not a value you embed inside the JSON — when you reference paths in args, write them out fully.

npx and PATH

The Claude Desktop process inherits a minimal environment. If you installed Node via fnm, nvm-windows, or another version manager, the GUI app may not see npx on PATH and will log:

[error] Failed to spawn server: 'npx' is not recognized

Fixes:

1. Install Node.js from nodejs.org (the system installer adds itself to user PATH that GUI apps see).
2. Or, replace "command": "npx" with the absolute path: "command": "C:\\Program Files\\nodejs\\npx.cmd".

uvx on Windows

The fetch server uses uvx. After installing uv with the PowerShell one-liner, restart your terminal and verify with uvx --version. Same PATH caveat applies — for Claude Desktop, you may need to use the absolute path: "command": "C:\\Users\\me\\.local\\bin\\uvx.exe".

Line endings in the config file

Use LF (not CRLF) inside the JSON file. Notepad++, VS Code, and Cursor all default to LF; only old Windows Notepad still inserts CRLF. CRLF inside JSON string values can cause parser oddities in some clients.