15 years later... an AI-assisted refactor of the modern rewrite of the app that started it all.
The original Simple Coin Flip landed on Android in 2011. In 2023 it was thrown away and rebuilt from scratch as a MAD (Modern Android Development) app. In 2026 that rewrite got taken apart and put back together again — this time with a coding assistant doing the typing.
It is still, fundamentally, an app that shows you a picture of a coin.
Available on the Google Play Store.
Tap the coin or shake the phone. It flips, lands, and tells you which side came up. That's the whole pitch, and everything else exists to make that one interaction pleasant:
- 82 coins to flip — all 51 state quarters (District of Columbia included), the George Washington dollar, JFK half-dollar and Sacagawea dollar, 24 national euro designs, the Canadian loonie and toonie, a two-headed dollar for when you'd rather not leave things to chance, and a Claude Code coin. Or pick Random and let the app choose a different one every flip.
- Favorites — star the coins you actually use and they collect in their own section at the top of the picker, so you're not scrolling past every state quarter to find the loonie.
- Your own coin — put your own artwork on the two faces. Pick a photo, frame it in a circular crop with pan, zoom, rotate and mirror, and it joins the picker pinned to the top of your favorites. The app rings it in the same colors it writes HEADS and TAILS in, so an arbitrary picture still reads as a coin — switch the ring off if you photographed a real one.
- Custom labels — call the sides whatever you like. Yes / No, Beer / Tacos, Ship / Crown.
- Heads and tails tallies, with a quick-reset button if you want it.
- Streaks — turn it on and a run of identical results counts up beside the result as HEADS ×7. Your best run for each side is kept in Settings, and setting a new record of ten or more plays a fanfare.
- Material You dynamic color on Android 12+, light and dark, portrait and landscape.
- Secure random — swap
kotlin.random.Randomforjava.security.SecureRandomif you have strong feelings about entropy sources in a coin-flipping app. (You might!) - A diagnostics screen that flips the coin up to ten million times and reports the distribution, for exactly those people.
- 13 languages, and sound, haptics and animation you can each turn off.
Single-module Kotlin app, Jetpack Compose throughout, MVI-ish state management.
| UI | Jetpack Compose (Material 3), one Activity hosting Navigation Component fragments that each render a Compose screen |
| State | Per-feature State / Action / Effect triads; ViewModels expose StateFlow and a SharedFlow of one-shot effects |
| DI | Hilt |
| Persistence | SharedPreferences behind a typed SettingsManager |
| Testing | JUnit 5, MockK, Kluent, Turbine |
| Coverage | Kover, reported into every CI run's summary |
| Toolchain | Versions live in gradle/libs.versions.toml; SDK levels in coinflip/build.gradle.kts |
The coin animation is the one deliberate holdout: it's still an ImageView driven by a frame-by-frame
AnimationDrawable, wrapped in an AndroidView. It was written that way in 2011, it works, and
nothing about Compose makes it better.
Two supporting documents are worth reading before touching related code:
- CLAUDE.md — architecture notes and the non-obvious constraints, aimed at coding agents
- I18N.md — which coin face is "heads" in each language, and the two idioms that run backwards
./gradlew :coinflip:assembleDebug./gradlew :coinflip:checkcheck runs the build, unit tests, Android lint and ktlint. CI runs the same thing on every pull
request and reports coverage into the run summary.
The 2026 refactor was done by Claude — landscape support, the rebuilt Settings screen, the searchable coin picker and favorites, custom coin faces, corrections to all 13 translations, the bulk of the unit test suite, the AGP 9 / Gradle 9 / SDK 37 migration, and most of the code in between — working from direction, design decisions, and on-device testing by @banasiak. The commit messages in that stretch were written by Claude as well, which goes some way toward explaining their length.
Coin images are from the United States Mint and the European Central Bank, except the Claude Code coin, which wears Claude Code's own mascot.
The source code is public domain, via the Unlicense. Do whatever you want with it.
The binaries are not: the coin images come from the sources named above and carry their own terms, which are not mine to waive.