Little Snitch

Little Snitch is a macOS application firewall and network monitor. It alerts you when an app attempts to connect to the internet, so you can allow or deny the connection, and it provides tools to inspect network activity.

• Review connection details such as data volume, server location, ports, and protocols, and explore activity in real time or over time.
• Organize and search connections by app, domain, or country; create rules for specific servers, domains, ports, or protocols.
• Use Silent Mode to allow new connections initially and decide about them later. Profiles and rule groups help organize rules and can be switched automatically based on Wi-Fi networks.
• The menu-bar Control Center gives access to recent activity, denied connections, and operating modes. The product also includes a command-line utility for tasks such as changing settings and exporting rules.

Install this Homebrew cask variant with brew install --cask little-snitch@5. It installs Little Snitch.app on macOS. This is the version-5 cask and conflicts with the little-snitch, little-snitch@4, and little-snitch@nightly casks. The developer describes a demo mode that provides the same protection and functionality as the full version; it runs for three hours at a time, can be restarted, and its Network Monitor expires after 30 days. A license key turns it into the full version.

Sources: Little Snitch · Homebrew cask