Some lessons let you write and run code right inside the course — no local setup needed.
Supported languages
- Python
- JavaScript
- TypeScript
Anything else is rejected with "Unsupported language".
Limits
- 20,000 characters of code per run.
- 5 seconds runtime — long-running loops will time out.
- 64 MB memory.
- Output is truncated at 20,000 characters.
Why was my code rejected?
Exercises run in a locked-down sandbox. File access, network calls, process spawning and similar operations are blocked — you'll see "Code contains restricted patterns". This keeps the environment safe for everyone; rewrite the exercise using only standard input and output.
Checked exercises
Some exercises compare your output with an expected result — match it exactly (watch spaces, line breaks and letter case).