Block an app from the internet, or just one company or domain for it

The fastest way: Ask FireAI

1. Open Home or the menu bar, and type into Ask FireAI.
2. To block an app entirely: “block Slack” (or your app’s name).
3. To block one company or domain for one app: “never let Slack talk to Datadog”, or name a domain directly, e.g. “block Teams from reaching doubleclick.net”.
4. FireAI shows a preview of exactly what it will change — click Apply, or Cancel if it got it wrong.

The precise way: Rules

1. Open Rules and click Add rule.
2. Pick Block (“Stop the connection”).
3. For Which app?, choose the app. To block it completely, set Which website or server? to Anywhere on the internet.
4. To only cut off one company or domain, set Which website or server? to “A website and all its subdomains” and type the domain, or “One website” for a single host.
5. Choose Always or Until I restart my Mac, then save.