Which CL implementation?

SBCL — one of the fastest and most-used free CLs.

Quicklisp / ASDF packages?

No — sandbox has no network. Standard library only.

Use them locally against your machine. Our editor is web-based.

Common Lisp · online compiler

Run Common Lisp online

Run Common Lisp online — SBCL, the workhorse CL implementation.

Version

Common Lisp 2

Firecracker microVM live per-test verdicts multi-file compile

Common Lisp is the industrial-strength Lisp: CLOS multi-methods, first-class macros, a condition system that makes exceptions look primitive. Still shipping in production at Grammarly, ITA, Franz.

ls-judge runs SBCL (Steel Bank Common Lisp) inside a Firecracker microVM.

Starter code

What you get in Common Lisp

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

common lisp

Common Lisp 2

(let ((n (parse-integer (read-line))))
  (write-line (write-to-string (* n 2))))

stdin →

expected →

FAQ

Common questions about Common Lisp on ls-judge

Which CL implementation?: SBCL — one of the fastest and most-used free CLs.
Quicklisp / ASDF packages?: No — sandbox has no network. Standard library only.
Free?: Yes.
Emacs / SLIME?: Use them locally against your machine. Our editor is web-based.