Insights on Jetpack Compose hot reload, Android, Compose UI development, and Compose HotSwan engineering.
Compose HotSwan 2.2.0 is out. On Android, a save that changes code inside a composable spends far less time in HotSwan (385 ms against 944 ms at the median, with the new path on and off), more of your on screen state survives an edit, and far fewer saves end with a warning they did not deserve. Here is what got faster, what now stays put, and the one step to take when you upgrade.
Compose HotSwan 2.0.0 is out. It ships its own interpreter engine, so a structural change goes around the runtime instead of being forced through it: add and remove composables, change how a screen branches, or replace an entire screen with new code, on a running app. One save now reaches Android, the iOS simulator, and Compose Desktop together, and an AI agent can drive the whole loop while you watch the device.
Compose HotSwan 2.0.0-beta04 brings hot reload to Compose Desktop (JVM) targets, running the same interpreter that drives Android. Select a device and your desktop app, save once, and both update in place with navigation and on screen state preserved. Here is what it looks like, how one engine drives two runtimes, and how to set it up.
Compose HotSwan v2 enters beta with a much wider hot reload range. Beyond tweaking values, you can restructure layouts, replace a whole screen with brand new code, and let an AI agent rewrite your app live on a running device through the HotSwan MCP server, with navigation and on screen state preserved. Here is how far it goes, how the reload works, and how to install the beta.
Your @Preview functions live in one editor, behind a recompile, on a renderer that does not match a phone. This walks through rendering a preview on a real device, capturing every preview into a browsable HTML catalog with captureAllPreviews, tuning the per preview render delay so slow screens still come out clean, running it all in GitHub Actions on a managed Android device, and publishing the catalog to GitHub Pages on every commit. With a working Pokedex Compose example, plus where Paparazzi and Roborazzi fit alongside it.
Side effects in Jetpack Compose are where the build-restart-navigate loop hurts most. A LaunchedEffect only fires when its key changes, so testing one means rebuilding, relaunching, and recreating the exact state that triggers it. With hot reload, you change the key or the body, save, and the effect re-runs immediately on the same screen. Walked through with two examples from Pokedex Compose.
Editing an AGSL shader source string at runtime usually means a full rebuild. With remember(SHADER_SRC) and HotSwan literal patching, every constant inside the shader and every Kotlin side knob becomes tunable on a running device. Walked through with a thin film soap bubble physics demo, originally by Kyriakos Georgiopoulos.
Choosing a Compose UI theme usually means editing colors in source, rebuilding for thirty seconds, judging by gut, and repeating. With HotSwan Palette, an AI agent fans out several theme variants live on your running app, captures a screenshot of each, and serves a side by side grid you pick from in the browser. See every option before you commit, no rebuilds. Walked through with Now in Android.
Animation development in Jetpack Compose means rebuilding your app for every tiny change to a duration, easing curve, or color value. With hot reload, you can tune animations by eye on a real device and see every change reflected in under a second.
Trace the full path from a one line code change to running pixels on an Android device. Explore Gradle task graphs, Kotlin incremental compilation, KAPT vs KSP, dexing, and where the time actually goes.
Android Studio's Compose Preview does not render the same pixels as a real device. Explore the layoutlib rendering engine, font divergence, image loading boundaries, system UI simulation, dynamic theming, and how to get pixel accurate previews on device.
A practical guide to preview driven development with Jetpack Compose. Learn how to structure previews that stay maintainable, avoid common pitfalls, and extend previews into on device rendering and automated screenshot catalogs with zero rebuild time.
Android developers spend more time waiting for builds than looking at their changes. HotSwan eliminates the build-wait-navigate loop by hot reloading Compose UI changes on a running device in under a second. No restart, no state loss, no navigation reset. This article covers how it works, what you can hot reload, and why it changes day to day Compose UI development.