OCaml · version 5

Run OCaml 5 online

OCaml 5 — run it in a Firecracker microVM on ls-judge. Real toolchain, no wrapper.

Starter code

What you get in OCaml 5

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

ocaml
OCaml 5
let () =
  let n = int_of_string (input_line stdin) in
  Printf.printf "%d\n" (n * 2)
stdin →21
expected →42
How it runs

How ls-judge runs OCaml 5

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 OCaml 5toolchain 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.