Describe the little tool you wish existed (a timer that hums every thirty seconds, a thing that tells you which plant needs water today) and the phone writes it for you. It lands in a spellbook only you can see. A cantrip is the smallest kind of spell, and these are about that big.
The model that writes them runs on the phone, so nothing leaves it. Each cantrip is just HTML in a private sandbox that can still reach your camera, location, haptics and notifications. You can hand one to a friend as a file.
What I learned / would do differently
A small coder model gets reliable when you give it less room. A tight HTML template, a fixed set of bridge calls, and a validator that throws out anything else. Coaxing it with better prompts never got close. Runs on iPhone 13 or newer.
Go see Cantrip
Available now on the App Store.