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setting-up-compose-hotswan

Coding & development

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Updated 10-16 01:07

About this skill

Setting Up Compose HotSwan: zero to sub-second reload on a real device

Compose HotSwan is a JetBrains IDE plugin plus a Gradle compiler plugin that swaps changed Kotlin classes into a running Compose app on a real device or emulator in under one second, preserving navigation, scroll, and remember state. This skill installs both pieces, wires the canonical Gradle DSL with debugOnly = true, and verifies the first save-to-reload round-trip. Sibling skills cover what does and does not hot-reload (../understanding-hot-reload-limits/SKILL.md), state preservation across reloads, and the AI-driven iteration loop.

Versions verified at the time of authoring. Confirm against the current release notes for newer minors.

When to use this skill

  • The developer mentions HotSwan, hot reload, instant UI update, "save and see", "no rebuild", live edit, or fast Compose iteration on device.
  • The developer has the HotSwan JetBrains Marketplace plugin installed and asks how to apply the Gradle compiler plugin.
  • A team is onboarding a new project to HotSwan and wants the canonical libs.versions.toml + root build + app build wiring.
  • The developer just installed the IDE plugin and the tool window status is stuck before WATCHING.

When NOT to use this skill

  • The question is about JetBrains' own Live Edit or Apply Changes features. HotSwan and those are separate products with different boundaries; do not conflate.
  • The question is about Compose Preview rendering inside the IDE. HotSwan targets the running app on a real device or emulator, not preview canvases.
  • The question is about which changes hot-reload vs force a rebuild. See ../understanding-hot-reload-limits/SKILL.md.
  • The question is about preserving complex state across reloads. See the state-preservation sibling skill (out of scope here).

Prerequisites

  • Android Studio 2024.3+ or IntelliJ IDEA 2024.3+.
  • Kotlin 2.0+ with the org.jetbrains.kotlin.plugin.compose Gradle plugin already applied on the Compose modules.
  • Gradle 8+.
  • A real device or emulator with USB debugging enabled and visible to adb devices.
  • The HotSwan IDE plugin installed from JetBrains Marketplace (https://plugins.jetbrains.com/plugin/30551-compose-hotswan/).

Workflow

  1. Declare the plugin in libs.versions.toml so the version pins centrally:

    [plugins]
hotswan-compiler = { id = "com.github.skydoves.compose.hotswan.compiler", version = "1.2.10" }

    Pin 1.2.10 (latest verified at the time of authoring). Check the HotSwan releases page for newer stable versions before adopting; HotSwan iterates frequently and a newer minor often ships compatibility for a newer Compose runtime. The plugin id is com.github.skydoves.compose.hotswan.compiler exactly. Do not swap the com.github prefix for any other vendor namespace; HotSwan is published under com.github.skydoves.

  2. Apply at the root build.gradle.kts with apply false so the plugin is resolved once but only attaches to modules that opt in:

    plugins {
    alias(libs.plugins.hotswan.compiler) apply false
}

  3. Apply in each Compose app module's build.gradle.kts:

    plugins {
    alias(libs.plugins.android.application)
    alias(libs.plugins.kotlin.android)
    alias(libs.plugins.kotlin.compose)
    alias(libs.plugins.hotswan.compiler)
}

  4. Configure the canonical DSL block in the same module file. The capital S in hotSwanCompiler is part of the identifier:

    hotSwanCompiler {
    enabled = true
    debugOnly = true
}

    debugOnly = true is the default and the rule for production. Release builds MUST NOT carry the HotSwan transformations.

  5. Sync Gradle. The build should resolve without errors. Confirm the plugin attached by inspecting the build's plugin list (./gradlew :app:buildEnvironment or the IDE Gradle tool window).

  6. Open the HotSwan tool window via View -> Tool Windows -> HotSwan. Click Start. The status indicator should change to READY.

  7. Run the app normally with the Run action. Once the app process connects, the tool window status moves from READY to WATCHING.

  8. Make a body-only edit and save. Change the color or text inside one composable function body, then save the file. The change should appear on device in under one second; navigation, scroll position, and remember values stay intact.

  9. If the change does not appear, fall through to the troubleshooting checklist below before changing any Gradle configuration.

Patterns

Pattern: configure with debugOnly true (production safety)

// WRONG
hotSwanCompiler {
    enabled = true
}
// WRONG because: omitting `debugOnly = true` allows the HotSwan transformations to attach to release
// builds. They are diagnostic-only and MUST NOT ship in production.

// RIGHT
hotSwanCompiler {
    enabled = true
    debugOnly = true
}

Pattern: respect the capital S in the DSL block name

// WRONG
hotswanCompiler {
    enabled = true
    debugOnly = true
}
// WRONG because: the extension is hotSwanCompiler with a capital S in the middle. Lowercase will
// not resolve and Gradle reports an unknown extension.

// RIGHT
hotSwanCompiler {
    enabled = true
    debugOnly = true
}

Pattern: apply at root with apply false, in modules with alias(...)

// WRONG (root build.gradle.kts)
plugins {
    alias(libs.plugins.hotswan.compiler)
}
// WRONG because: applying at the root project triggers the compiler plugin everywhere, including
// modules without Compose. Use apply false at the root and alias(...) inside each Compose module.

// RIGHT (root build.gradle.kts)
plugins {
    alias(libs.plugins.hotswan.compiler) apply false
}

// RIGHT (app/build.gradle.kts; Compose module)
plugins {
    alias(libs.plugins.android.application)
    alias(libs.plugins.kotlin.android)
    alias(libs.plugins.kotlin.compose)
    alias(libs.plugins.hotswan.compiler)
}

hotSwanCompiler {
    enabled = true
    debugOnly = true
}

Pattern: do not depend on HotSwan at the source level

// WRONG
import com.github.skydoves.compose.hotswan.runtime.HotReloadable

@HotReloadable
@Composable
fun Greeting() { Text("Hello") }
// WRONG because: HotSwan is a build-time and IDE-time tool. Production code must not import
// HotSwan runtime classes or annotations; the Gradle plugin attaches transformations during
// compilation without requiring source-level coupling.

// RIGHT
@Composable
fun Greeting() { Text("Hello") }

Pattern: canonical three-file setup (paste-ready)

# gradle/libs.versions.toml
[plugins]
hotswan-compiler = { id = "com.github.skydoves.compose.hotswan.compiler", version = "1.2.10" }

// build.gradle.kts (root)
plugins {
    alias(libs.plugins.android.application) apply false
    alias(libs.plugins.kotlin.android) apply false
    alias(libs.plugins.kotlin.compose) apply false
    alias(libs.plugins.hotswan.compiler) apply false
}

// app/build.gradle.kts
plugins {
    alias(libs.plugins.android.application)
    alias(libs.plugins.kotlin.android)
    alias(libs.plugins.kotlin.compose)
    alias(libs.plugins.hotswan.compiler)
}

hotSwanCompiler {
    enabled = true
    debugOnly = true
}

Troubleshooting

  • Status stuck at READY after Run. The device is not connected. Run adb devices and confirm the device or emulator is listed; reconnect USB or restart the emulator.
  • Status WATCHING but no reload on save. The save was a structural change (parameter, constructor, interface, inline function, new resource id). Cross-link ../understanding-hot-reload-limits/SKILL.md to identify the boundary.
  • Reload happens but state is lost. The change cascaded to a tier-2 (composition reset) or tier-3 (Activity.recreate()) recomposition. Cross-link the state-preservation sibling skill once available.
  • The hotSwanCompiler { ... } block does not resolve. Gradle did not sync after adding the plugin. Re-sync; verify Kotlin 2.0+ is the active Kotlin version on the module; verify the alias matches the entry in libs.versions.toml.

Mandatory rules

  • MUST set debugOnly = true. HotSwan transformations are diagnostic-only and MUST NOT ship in release builds.
  • MUST apply the Gradle plugin only on Compose modules. Apply at the root project with apply false so non-Compose modules are not transformed.
  • MUST NOT depend on HotSwan classes at the source level. No annotations, no runtime imports. HotSwan is a build-time and IDE-time tool; production code stays pure.
  • MUST NOT mix HotSwan with a stale Compose Compiler. Verify org.jetbrains.kotlin.plugin.compose is applied on Kotlin 2.0+ before adding HotSwan.
  • MUST pin the HotSwan version in libs.versions.toml so all Compose modules in the project use a single version. The latest verified version is 1.2.10; check hotswan.dev/docs/releases for newer stable releases before pinning.
  • PREFERRED: combine HotSwan with the AI iteration loop sibling skill (../iterating-with-ai-and-mcp/SKILL.md) once the developer is comfortable with manual hot reload and wants Claude to drive the edit-reload-screenshot cycle via MCP.

Verification

  • ./gradlew :app:buildEnvironment lists the com.github.skydoves.compose.hotswan.compiler plugin among applied plugins.
  • The HotSwan tool window status reads WATCHING after the app launches with Run.
  • Editing a Text color inside a composable and saving the file changes the color on device within one second.
  • remember values, scroll position, and the navigation back stack survive the change.
  • A release build (./gradlew :app:assembleRelease) does not include HotSwan transformations. Verify by confirming debugOnly = true is set, or by inspecting the release dex with dexdump for the absence of HotSwan-injected helper classes.
  • No production source file in the module imports a com.github.skydoves.compose.hotswan.* symbol (grep -R "com.github.skydoves.compose.hotswan" src/main/ returns zero hits).

References