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Online Kotlin Compiler
Write, compile, run, and debug Kotlin code online in a full-featured browser IDE. Work with multiple files, save your workspace, and collaborate in real time.
🚀 71,259 total executions (378 this month)
Practice Python with coding challenges
Solve hands-on problems right in this editor: run the sample tests, submit, and get an AI code review.
🧩 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.
More than a code runner
Use a multi-file editor, an isolated execution terminal, runtime-specific libraries, persistent workspaces, sharing, and real-time collaboration from the same executor.
How to use this executor?
Choose a runtime, open or create a file, write your code, and select Run. Output appears in the terminal, while signed-in users can keep files in a workspace, install libraries, and collaborate through shares.
- Select a version and edit the current file or open another workspace file.
- Run the code, provide input in the terminal when requested, and review saved run history.
- Use libraries, workspace tools, sharing, and chat when your task needs more than one snippet.
💡 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 = 1002. 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)