MCPmatic

How to add an MCP server to Claude Desktop and Cursor

Published · Updated · Written against MCP spec 2026-07-28

Both Claude Desktop and Cursor read MCP servers from a JSON file with an mcpServers object. Here's where the files are and what goes in them.

Claude Desktop#

The config file is claude_desktop_config.json:

  • macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
  • Windows: %APPDATA%\Claude\claude_desktop_config.json

A local server started with npx, adapted from the MCP docs' filesystem server example:

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/Users/username/Desktop"]
    }
  }
}

Fully quit and restart Claude Desktop after editing the file. If a server doesn't show up, the MCP logs are in ~/Library/Logs/Claude/mcp*.log on macOS.

Cursor#

  • Project only: .cursor/mcp.json in the project folder
  • All projects: ~/.cursor/mcp.json
{
  "mcpServers": {
    "my-api": {
      "command": "node",
      "args": ["${workspaceFolder}/mcp-server/index.js"],
      "env": { "MY_API_KEY": "${env:MY_API_KEY}" }
    }
  }
}

Cursor resolves variables such as ${env:NAME}, ${userHome} and ${workspaceFolder} in command, args, env, url and headers. Remote servers use a url instead of a command.

Keep keys out of the file#

A project .cursor/mcp.json is often committed to git. Reference environment variables (as above) rather than pasting API keys, and add any local-only config to .gitignore. The same applies to tool arguments: credentials belong in the server's environment, not in parameters the model fills in. The linter flags credential-looking parameters.

Only run servers you trust#

A local MCP server is a program running with your permissions. The spec's security guidance warns about malicious startup commands in client configs and malicious server packages. Check where a server comes from before adding it, and see MCP security best practices.

Sources#

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