Kotlin online compiler

What runs your code

Good to know

• Compiles with kotlinc into a jar that runs on Java 25, so fun main() is all a program needs.
• readln() reads the next line of the Input tab; readlnOrNull() returns null at the end.
• Compiling takes most of a run's time, more than in any other language here except F#.

Run Kotlin from your own code

Send the code and its input to the sync endpoint with an API key, and the output comes back in the response. The API docs cover the async endpoint with callbacks and every response field.

curl -X POST https://api.onlinecompiler.io/api/run-code-sync/ \
  -H "Authorization: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "compiler": "kotlin-2.4",
    "code": "fun main() {\n    val name = readln()\n    println(\"Hello, $name!\")\n}",
    "input": "Ada"
  }'

The response has output ("Hello, Ada!\n" here), error, exit_code, time and memory.

Put a runnable Kotlin example on your site

The editor above is the embeddable widget. Add the script and a div with your widget key, and your readers can edit and run the code without an account:

<script src="https://onlinecompiler.io/widget.js"></script>

<div class="runcode" data-key="YOUR_WIDGET_KEY" data-lang="kotlin-2.4">
  <script type="text/plain">
    fun main() {
        val name = readln()
        println("Hello, $name!")
    }
  </script>
</div>

On a platform that takes an iframe but not a script, such as many course sites, use the iframe embed. For Docusaurus, MkDocs, Sphinx and Mintlify, see runnable code examples in docs.

Other languages

Python, C, C++, Java, C#, F#, Go, Rust, PHP, Ruby, Haskell, TypeScript, JavaScript, SQL, Bash, Fortran, Visual Basic, R.

Frequently asked questions

Is this Kotlin online compiler free?

Yes. Running Kotlin on this page needs no account and shows no ads. To run Kotlin from your own app or site, the API and the widget are free up to 100,000 runs a month, commercial use included.

Can my Kotlin program read input?

Yes. Type it in the Input tab before you run, and the program reads it from standard input. The whole input is sent when you press Run, so a program can't ask for more while it runs.

Can I use Kotlin libraries?

The Kotlin standard library and the Java 25 class library. kotlinx libraries such as coroutines aren't included, and programs have no network access.

How long can a program run?

Up to 30 seconds, with 512 MB of memory and 2 CPUs. A program still running at 30 seconds is stopped with exit code 124, and output over 64 KB per stream is cut.

Where does my code run?

On our servers, in a fresh gVisor sandbox with no network access that is deleted when the run ends. Each run is kept in execution history with its output; the security page says what is stored.