On the web, a save updates the page in place. On iOS and Android there is no JavaScript engine on the device to patch, because PMTC compiles your shared source to real SwiftUI and Jetpack Compose. So the native loop is a rebuild loop, not hot reload: the app restarts and in-memory state resets. pyreon-native dev makes that loop as short as the toolchains allow.

The three-layer loop

Use the cheapest layer that answers your question.

pyreon-native dev

# iOS: uses a booted simulator, or boots the newest iPhone simulator
npx pyreon-native dev --target=ios

# Android: needs an online emulator or a USB-debugging device
npx pyreon-native dev --target=android

Run it from the project root of a Create Multi-Platform app. It does this on every change:

1. Compiles your source in memory and prints compiler warnings and errors straight away, before any Xcode or Gradle work starts. A compile error never reaches the native toolchain, and the watcher keeps running.

2. Decides whether a native build is needed. If the emitted Swift or Kotlin is byte-identical to what the running app was built from (a comment, whitespace, a web-only file), the build is skipped.

3. Builds incrementally: xcodebuild against a persistent derived-data folder on iOS, gradle installDebug on Android.

4. Installs and relaunches the app by its bundle id or application id, replacing the running copy.

What triggers what:

A failed build prints the tail of the tool's output and waits. Fix the problem and save again: a failed build is never remembered as "up to date", so the next save always retries.

Options

Measured timings

Measured on an Apple-silicon Mac, iOS 18.5 simulator, with the scaffolded counter app. A larger app has more Swift to compile, so treat these as a floor and measure your own.

The Android numbers depend far more on the machine and on Gradle's daemon state; the first Gradle run also downloads and configures dependencies.

What it does not do

• No hot reload and no state preservation. The app restarts on every native rebuild. Keep the state you are iterating on cheap to reach, or iterate on it in the web build.

• No source-mapped native errors. A Swift or Kotlin compiler error is shown as the toolchain reports it, against the generated file. The generated files start with a source-location comment pointing at your .tsx.

• No emulator creation. It boots an existing iOS simulator if none is running; for Android, start an emulator or connect a device first.

• No physical-device deployment. It targets simulators and emulators. A physical device needs signing, which is part of release builds (see Create Multi-Platform), not the edit loop.

• Autodetected project identity. The iOS project name and bundle id come from ios/project.yml; the Android application id and launcher activity come from android/app/build.gradle.kts and the manifest. A project restructured away from the scaffold's layout will be refused with a message naming the missing file.

Troubleshooting

• "no iPhone simulator is installed" — add one in Xcode → Settings → Platforms.

• "no Android device is online" — start an emulator (Android Studio → Device Manager) or plug in a device with USB debugging, then check adb devices.

• "adb is unavailable" — install the Android SDK platform-tools and set ANDROID_HOME.

• The Android build cannot find Java — put a JDK 17 on PATH (or set JAVA_HOME) before starting.

• Nothing happens after a save — the watcher ignores generated output, node_modules and build folders by design. A file outside src/, assets/, web/, ios/ and android/ is not watched.