Online Kotlin Compiler

Write, run, and share code snippets - no setup required.

Main.kt

Alice
30

Output

Click Run to see the output here.

fun main() {
    val name = readLine()!!
    val age = readLine()!!.toInt()
    println("Hello, $name! You are $age years old.")
}

Write, compile, and run Kotlin online

A free online Kotlin compiler and playground. Type Kotlin in your browser, press Run, and the Kotlin compiler builds and executes your program in seconds. No JDK, no IntelliJ IDEA, no Android Studio, and no Gradle project to set up first.

The editor uses the same engine as VS Code, so Kotlin syntax highlighting and autocompletion work out of the box. Code compiles with the official Kotlin/JVM compiler in a sandboxed container, so you get the real language - null safety, when expressions, data classes, lambdas, and the full standard library. The sample program reads two lines from stdin, which is what you need for interview problems and command-line exercises.

What makes this Kotlin compiler useful

Instant compile and run - write Kotlin, press Run, and see stdout and any compiler errors in seconds, on desktop or phone.
Kotlin syntax highlighting and autocompletion in the same editor engine VS Code uses, with clear compiler diagnostics when something doesn't type-check.
Stdin input is supported: readLine() and readln() read from the playground's input box, so command-line programs and coding-interview solutions work end to end.
The real Kotlin/JVM compiler and standard library - collections, string templates, extension functions, data classes, sealed classes, and coroutines-free concurrency basics all run as they would locally.

What you can build in the Kotlin playground

Null safety in practice: nullable types, the safe-call operator ?., the Elvis operator ?:, and smart casts, tested one line at a time with no Android project around them.
Collections and lambdas: map, filter, groupBy, sortedBy, and fold over lists and maps - the functional core of everyday Kotlin.
Algorithms and interview problems that read input from stdin, plus quick experiments with data classes, when branches, ranges, and extension functions.

Online Kotlin compiler FAQ

Is the online Kotlin compiler free?

Yes, the Kotlin playground is free to use with no sign-up. Open the page, write your code, and run it. There is no JDK, IntelliJ, or Android Studio to install.

Do I need Android Studio or the JDK installed?

No. Kotlin compiles and runs on our servers, so nothing is installed on your machine. That makes this a quick way to test a snippet from a Chromebook, a tablet, a locked-down work laptop, or any computer where you can't set up a toolchain.

Can I read input from stdin in the Kotlin playground?

Yes. Type your input lines in the input box and read them with readLine() or readln() exactly as you would when running a compiled program in a terminal. The starter program does this - it reads a name and an age and prints a greeting.

Which Kotlin version does the compiler use?

The playground uses the official Kotlin/JVM compiler with the standard library, so modern language features - when with subject-less branches, data classes, sealed classes, extension and infix functions, trailing lambdas, and destructuring - all work. Android-only APIs are not available, since there is no Android runtime; everything in the Kotlin standard library is.

How do I learn Kotlin after trying the compiler?

Edit the sample code, press Run, and iterate. When you want something more structured, Coddy's free interactive Kotlin course covers null safety, when, loops, functions, and collections with hands-on exercises and a certificate at the end - a solid base before Android or Ktor.

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Free, browser-based tools that pair well with the Kotlin Playground - all part of Coddy.

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