Notes
What I learn making small iPhone apps: fixes, numbers, decisions, and the caffeine math behind Onset.
How I run a one-person app studio with AI coding agents
Essay · 3 minThe rules behind a solo iPhone studio where Claude Code, Codex and Grokbot write much of the code, and the breakages that produced each rule.
TestFlight testers said my app looked "vibe coded." Here's what I changed.
Case study · 2 minFive changes to Onset, a caffeine tracker for iPhone, after TestFlight feedback. Nearly every one removed something.
Two iOS 26 Liquid Glass bugs, and the fixes
Fix · 2 minOn iOS 26, Liquid Glass in a safeAreaBar makes the tab bar snap instead of morph, and toolbar buttons get a circle inside a circle. Both fixes, with SwiftUI code.
ITMS-90111: Apple rejected my build because of my Mac, not my code
Fix · 2 minAn App Store build made with a supported Xcode still failed with ITMS-90111, because the Mac ran a macOS beta. What happened and the fix.
I checked my app's Starbucks caffeine numbers against Starbucks. 23 had changed.
Data · 3 minOnset's caffeine catalog checked against manufacturer pages: 60 products and 103 servings. The 23 Starbucks amounts that changed, old and new.
How I decide which app ideas to build
Essay · 3 minFive questions every app idea answers before I build it, including whether a chatbot could do 80% of it, and the app I dropped too early.
Turning Apple Health sleep samples into nights
Guide · 2 minHealthKit gives you sleep samples, not nights. The five rules Onset uses to turn them into one night per morning, with the Swift code.
Why I tried estimating caffeine during the first half of the night
Case study · 2 minWhy an early Onset 1.3 design focused on average caffeine in the first half of the night, what the research does and doesn't show, and what changed later.
Onset: checking the next drink before you have it.
Case study · 4 minWhy Onset lets you preview a drink before logging it.
How long does caffeine stay in your system?
Guide · 3 minHalf-life, overlapping drinks, and the limits of an estimate.
How many hours before bed should you stop caffeine?
Guide · 5 minA look at drink timing, research, and estimated caffeine at bedtime.
How to track caffeine on iPhone with Onset
Walkthrough · 3 minA walkthrough of logging a drink, checking an estimate, and reviewing your history.