Run Dart 3 online

What you get in Dart 3

Clicking "Run now" opens the playground with this exact code and a matching test case — passes on first Run.

import 'dart:io';
void main() {
  final n = int.parse(stdin.readLineSync()!.trim());
  print(n * 2);
}

How ls-judge runs Dart 3

Every submission is compiled and executed inside its own Firecracker microVM — the same isolation primitive AWS Lambda uses. No shared container, no shared kernel with other users' code. The Dart 3toolchain shipped with the microVM is the real thing (not a browser-side emulation): syscalls behave the way they do in production, and the compile / runtime behaviour matches what you would see on your own machine with that version installed.

Feed stdin from the Tests panel, watch verdicts stream per test case over a WebSocket. Free to use, no sign-up, works from any browser.