Run Ruby 3.4 online

What's in Ruby 3.4

• The `it` keyword — refer to a single block parameter without `|x|` declaration boilerplate.
• Prism replaces the traditional parser: better error messages and IDE-friendly ASTs.
• YJIT is now enabled by default with a smaller memory footprint and better warmup.

What you get in Ruby 3.4

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

n = gets.chomp.to_i
puts n * 2

How ls-judge runs Ruby 3.4

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 Ruby 3.4toolchain 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.