How to block an app from the internet on a Mac
What the built in macOS firewall can and cannot block, why it does not stop outgoing connections, and the options that do.
Can the macOS firewall block an app from the internet?
Not for outgoing traffic. The firewall in System Settings, Network, Firewall controls incoming connections only; an app can still connect out.
How do I stop an app connecting out?
Use an outgoing firewall app that asks per connection, or block the app's servers on your router. Quitting the app, or removing its login and background items, stops it at the source: login items.
How do I see what an app connects to?
nettop -P -L 1Activity Monitor's Network tab also shows how much each process sends and receives.
Common questions
Does Mac firewall block outgoing connections?
No. It blocks incoming connections only.
How do I block an app from accessing the internet on macOS?
Use an outgoing firewall app, router rules, or stop the app from running in the background.