Kotlin Toolchain 0.12: Multiplatform Library Publishing, Wasm Apps, and More

Summary

Kotlin Toolchain 0.12.0 extends its multiplatform build and publishing capabilities with multiplatform library publication, preview support for Wasm applications, command-line Compose Hot Reload, and broader IDE and terminal improvements. Libraries use the existing publishing configuration and produce a common API, per-platform artifacts, sources, module metadata, plus commonized and platform-specific cinterop bindings; Compose Multiplatform resources are not yet included. wasm-js/app modules can be built into ready-to-use web applications, run with kotlin run, customized through resources, and supplied transitive npm dependencies from Kotlin Multiplatform libraries. The release also reduces default Maven Central files, supports Compose Hot Reload through an MCP server, and recommends project-root-relative // dependencies while retaining the older syntax. It raises minimum compilation requirements to JDK 17 and Kotlin 2.2.20, updates bundled versions including Kotlin 2.4.10 and JDK 25, and recommends IntelliJ IDEA 2026.2.1 or newer for the latest features.

Takeaways

1. 1

   Multiplatform publication includes the common API, one artifact per platform, sources, module metadata, and both commonized and per-platform cinterop bindings. Compose Multiplatform resources are not included yet.

2. 2

   wasm-js/app modules can be built into ready-to-use web applications, run with kotlin run, customized through index.html and other resources, and supplied transitive npm dependencies from Kotlin Multiplatform libraries.

3. 3

   Compilation now requires JDK 17 or newer and Kotlin 2.2.20 or newer; settings.jvm.release can still target a lower runtime, and the default versions include Kotlin 2.4.10 and JDK 25.