I recently built a small iPhone app called FocusLock.

The idea is simple: choose distracting apps, create a rule, and let the phone enforce the boundary when it is time to focus.

I built it because I kept running into the same problem with my own phone habits. I did not need a bigger productivity system. I needed fewer tiny negotiations with myself.

This post is mostly about the technical side: what it is like to build this kind of app on iOS, what Apple gives you through the Screen Time APIs, and the tradeoffs I ran into while building the first version.

The main frameworks

FocusLock is built around a few Apple frameworks:

FamilyControls

ManagedSettings

DeviceActivity

UserNotifications

SwiftUI

At a high level:

FamilyControls lets the user choose apps or app categories through Apple's system picker.

ManagedSettings lets the app apply shields to the selected apps/categories.

DeviceActivity lets the system wake an extension when a scheduled interval starts or ends.

The important detail is that…