Get started with Kotlin/Wasm and WASI

This tutorial demonstrates how to run a simple Kotlin/Wasm application using the WebAssembly System Interface (WASI) in various WebAssembly virtual machines.

You can find examples of an application running on Node.js, Wasmtime Deno, and WasmEdge virtual machines. The output is a simple application that uses the standard WASI API.

Currently, Kotlin/Wasm supports WASI 0.1, also known as Preview 1. Support for WASI 0.2 is planned for future releases. Follow this YouTrack issue for updates on WASI 0.2 support.

The wasmWasi target uses the new exception handling proposal by default, ensuring better compatibility with modern WebAssembly runtimes.

Before you start

Download and install the latest version of IntelliJ IDEA.
Clone the Kotlin/Wasm WASI template repository by selecting File | New | Project from Version Control in IntelliJ IDEA.
You can also clone it from the command line:
git clone git@github.com:Kotlin/kotlin-wasm-wasi-template.git

Run the application

Open the Gradle tool window by selecting View | Tool Windows | Gradle.
In the Gradle tool window, you can find the Gradle tasks under kotlin-wasm-wasi-example once the project loads.
You need at least Java 11 as your Gradle JVM for the tasks to load successfully.
From kotlin-wasm-wasi-example | Tasks | kotlin node, select and run one of the following Gradle tasks:
- wasmWasiNodeDevelopmentRun to run the application in Node.js.
- wasmWasiWasmtimeDevelopmentRun to run the application in Wasmtime.
- wasmWasiDenoDevelopmentRun to run the application in Deno.
- wasmWasiWasmEdgeDevelopmentRun to run the application in WasmEdge.
  When using Deno on a Windows platform, ensure deno.exe is installed. For more information, see Deno's installation documentation.

Alternatively, run one of the following commands in the terminal from the kotlin-wasm-wasi-template root directory:

To run the application in Node.js:
./gradlew wasmWasiNodeDevelopmentRun
To run the application in Wasmtime:
./gradlew wasmWasiWasmtimeDevelopmentRun
To run the application in Deno:
./gradlew wasmWasiDenoDevelopmentRun
To run the application in WasmEdge:
./gradlew wasmWasiWasmEdgeDevelopmentRun

The terminal displays a message when your application is built successfully:

Test the application

You can also test that the Kotlin/Wasm application works correctly across various virtual machines.

In the Gradle tool window, run one of the following Gradle tasks from kotlin-wasm-wasi-example | Tasks | verification:

wasmWasiNodeTest to test the application in Node.js.
wasmWasiWasmtimeTest to test the application in Wasmtime.
wasmWasiDenoTest to test the application in Deno.
wasmWasiWasmEdgeTest to test the application in WasmEdge.

Alternatively, run one of the following commands in the terminal from the kotlin-wasm-wasi-template root directory:

To test the application in Node.js:
./gradlew wasmWasiNodeTest
To test the application in Wasmtime:
./gradlew wasmWasiWasmtimeTest
To test the application in Deno:
./gradlew wasmWasiDenoTest
To test the application in WasmEdge:
./gradlew wasmWasiWasmEdgeTest

What's next?

Join the Kotlin/Wasm community in Kotlin Slack:

Join the Kotlin/Wasm community

Try more Kotlin/Wasm examples:

25 August 2026