Runs a shell command on the user's Mac and returns its output. Always active. Disabled when LMCP is in read-only mode. Dangerous commands (sudo, recursive deletes of system/home paths, disk formatting, shutdown/reboot, piping a downloaded script into a shell, fork bombs, daemon control) are refused. Commands run in a macOS sandbox with the same protected locations as file_read/file_write: credentials (keychains, ~/.ssh private keys, ~/.aws, ~/.config/gh, browser logins, another user's home) can't be read, and Local MCP's own settings, LaunchAgents and shell startup files can't be written; a command that names one is refused up front. CLIs that read their own credential file (aws, kubectl, gh with a file token) work only if the user adds that exact path to "fs_read_sensitive_allow" in Local MCP's config.json; keychain items stay out of reach. Inside the sandbox SwiftPM needs --disable-sandbox. Destructive: it previews the command first — pass confirm:true to actually run it. Output and runtime are capped.