Command Line Arguments

Command Line Arguments (CLI args) are the primary way local MCP servers are configured by their host applications. Since many MCP servers run as standalone executables over stdio, these arguments dictate the server's runtime environment.

Common Uses

• API Keys: Passing secrets required for the server to connect to external services (though environment variables are often preferred).
• Paths: Specifying root directories for a filesystem server.
• Port/Host: Configuring network settings for servers using SSE.

Configuration in HasMCP

In a mcp-config.json, arguments are defined in an array:

{
  "mcpServers": {
    "my-server": {
      "command": "node",
      "args": ["dist/index.js", "--verbose", "--root", "/data"]
    }
  }
}

Security Note

Sensitive data in CLI arguments might be visible in process listings on some operating systems. Use environment variables for highly sensitive secrets.

Questions & Answers

How are command line arguments used in the configuration of local MCP servers?

CLI arguments are the primary way host applications configure local servers running over stdio. They specify parameters like script paths, working directories, and runtime flags.

Where are these arguments typically defined in an MCP-compliant application?

They are usually defined in a configuration file (like mcp-config.json or claude_desktop_config.json) within an args array associated with the server's command.

What is a key security consideration when passing sensitive data via command line arguments?

Sensitive data (like API keys) in CLI arguments can sometimes be seen in system process listings. It is generally more secure to use environment variables for sensitive secrets.