Half of all "my MCP server won't load" problems come down to editing the wrong file. Here is exactly where each client keeps its MCP config, on every OS, and how to open it in one step.
Claude Desktop
File: claude_desktop_config.json.
- macOS:
~/Library/Application Support/Claude/claude_desktop_config.json - Windows:
%APPDATA%\Claude\claude_desktop_config.json - Linux:
~/.config/Claude/claude_desktop_config.json
Fastest way to open it: in Claude Desktop go to Settings → Developer → Edit Config. That button creates the file if it does not exist and opens the right one. Restart Claude after saving.
Cursor
- Global:
~/.cursor/mcp.json - Project-scoped:
.cursor/mcp.jsonin the project root
Or open Settings → MCP → Add new MCP server to edit it through the UI. Project config overrides global for that workspace.
Windsurf
File: ~/.codeium/windsurf/mcp_config.json. In the app, open the Cascade panel → MCP section → it links straight to the file. Hit Refresh after editing.
VS Code (Copilot)
VS Code uses a .vscode/mcp.json in the workspace, or the user settings.json under an mcp block. Use the command palette → MCP: Add Server to scaffold it.
Claude Code (CLI)
No file to hand-edit by default — use the CLI: claude mcp add <name> ... or claude mcp add-json <name> '<json>'. It stores config in ~/.claude.json.
The schema is (almost) the same everywhere
All of them use a top-level mcpServers object keyed by server name. A stdio server looks like:
{
"mcpServers": {
"filesystem": {
"command": "npx",
"args": ["-y", "@modelcontextprotocol/server-filesystem", "/path"]
}
}
}
Remote servers use "url" instead of command/args.
Gotchas that break it
- Invalid JSON — one trailing comma and the whole file is ignored silently. Validate it.
- Editing the wrong scope — global vs project (Cursor), or a stale copy.
- No restart — most clients only read the config on launch.
- Windows paths — escape backslashes:
C:\\Users\\you\\project.
Next steps
Got the file right but the server still will not load? See Cursor MCP not working or Claude Desktop MCP not loading. New to all this? Start with how to install MCP on Claude Desktop.