New to Kotlin? We recommend checking out Kotlin Koans to get up to speed.

Local development

To run the code for your challenge locally, you’ll need mvn installed. Our test runners use mvn version 3.9.5 (as of November 2023).

The script for your challenge (like ./ will automatically compile your code using mvn package before executing it.

File structure

  • The files for your solution are placed in the src/main/kotlin directory.
  • src/main/kotlin/Main.kt contains the main function, which is what the test runner executes.

Adding more files

You can add more files and directories to src/main/kotlin. The test runner will include them when compiling your code.

For example, if you added a file at src/main/kotlin/Foo.kt, you could use it like so:

fun foo() {
    println("Hello world!")

By default, all files in src/main/kotlin are in the default package. If you want to extract files into a different package, you’ll need to add a package declaration to the top of the file.

Let’s say you wanted to extract Foo.kt into the package. You’d add the following to the top of Foo.kt:

package com.example

fun foo() {
    println("Hello world!")

Adding dependencies

You can add dependencies to your project by adding them to your pom.xml file.

For example, to add the gson library, add the following to the <dependencies> section in your pom.xml:


When you push your code next, the runner will automatically download the dependency.