Run Forth online

Run Forth online — stack-based, concatenative, browser-hosted.

Version

Firecracker microVM live per-test verdicts multi-file compile

Forth is the stack-based, extensible language behind decades of embedded systems, boot loaders (Open Firmware), and NASA spacecraft. Two-word REPL, tiny footprint, endlessly expressive.

ls-judge runs gforth (the GNU Forth) in a Firecracker microVM.

Starter code

What you get in Forth

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

forth

Forth 0

pad 64 stdin read-line drop drop pad swap evaluate 2 * . cr

stdin →

expected →

FAQ

Common questions about Forth on ls-judge

Which Forth?: gforth (GNU Forth).
ANS Forth compliant?: gforth is ANS-conformant with modern extensions.
Free?: Yes.
Entry filename?: main.fs — loaded via `gforth`.