Kotlin Online CLI Playground

Use a fast Kotlin shell in your browser to test code and validate logic without an IDE.

Version

Sample

🚀 26,360 total executions (1,847 this month)

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🧩 About This Kotlin Online Executor

The CodeUtility Kotlin Executor lets you write, compile, and run Kotlin code directly in your browser — no installation, IDE, or SDK setup required. It uses real Kotlin compilers running in isolated sandboxes for a safe and authentic execution experience.

This tool supports multiple Kotlin versions — 1.6, 1.9, and 2.1 — so you can explore syntax updates, test code compatibility, and experiment with modern language features like coroutines, data classes, and sealed interfaces.

It’s ideal for students learning Kotlin basics, Android developers experimenting with snippets, or backend engineers testing logic in a JVM environment without leaving the browser.

The environment runs each snippet inside a secure containerized runtime, ensuring consistent performance and safe code execution.

💡 How to Use This Tool

1. Choose a Kotlin version from the dropdown above the editor (1.6, 1.9, or 2.1).
2. Write or paste your Kotlin code directly into the editor area.
3. Click Run to compile and execute the code, with output shown in the console below.
4. When running, a Stop button will appear — click it to terminate execution early.
5. Use Fix Code to automatically correct syntax or indentation issues.
6. After fixing, a Fixes button appears — click it to review your recent corrections.
7. You can also Upload Kotlin files from your computer or Download your code for later use.
8. Each execution runs for up to 20 seconds to ensure stability and fair resource usage.

🧠 Tip: The Kotlin runtime supports standard libraries and common language features — making it great for testing algorithms, practicing functional programming, or validating Android and backend Kotlin code behavior in real time.

💡 Kotlin Basics Guide for Beginners

1. Declaring Variables and Constants

Kotlin uses val for immutable variables and var for mutable ones.

val name: String = "Alice"
var age: Int = 30
val pi = 3.14  // type inferred

// Constants
const val MAX_USERS = 100

2. Conditionals (if / when)

Use if expressions or when for multiple branches.

val x = 2
if (x == 1) {
    println("One")
} else if (x == 2) {
    println("Two")
} else {
    println("Other")
}

when (x) {
    1 -> println("One")
    2 -> println("Two")
    else -> println("Other")
}

3. Loops

Use for, while, and do-while for iteration.

for (i in 0..2) {
    println(i)
}

var n = 3
while (n > 0) {
    println(n)
    n--
}

4. Arrays

Kotlin supports arrays using the arrayOf() function.

val numbers = arrayOf(10, 20, 30)
println(numbers[1])

5. List Manipulation

Use mutableListOf for dynamic lists.

val nums = mutableListOf(1, 2, 3)
nums.add(4)
nums.removeAt(0)

for (n in nums) {
    print("$n ")
}

6. Console Input/Output

Use readLine() for input and println() for output.

print("Enter your name: ")
val name = readLine()
println("Hello, $name")

7. Functions

Functions use fun keyword with optional return type.

fun add(a: Int, b: Int): Int {
    return a + b
}

println(add(3, 4))

8. Maps

mutableMapOf stores key-value pairs.

val ages = mutableMapOf("Alice" to 30)
println(ages["Alice"])

9. Exception Handling

Use try, catch, and finally to handle errors.

try {
    val result = 10 / 0
} catch (e: ArithmeticException) {
    println("Error: ${e.message}")
}

10. File I/O

Use File from java.io for file operations.

import java.io.File

File("file.txt").writeText("Hello File")
val text = File("file.txt").readText()
println(text)

11. String Manipulation

Kotlin strings support many methods and interpolation.

val text = "Hello World"
println(text.length)
println(text.substring(0, 5))
println(text.contains("World"))

12. Classes & Objects

Kotlin classes are concise and support default constructors.

class Person(val name: String) {
    fun greet() = println("Hi, I'm $name")
}

val p = Person("Alice")
p.greet()

13. Null Safety

Kotlin distinguishes nullable and non-nullable types. Use ? and ?: for safety.

val name: String? = null
println(name?.length ?: 0)