Pick a mode, work through an exercise, then check it against the answer key.
Run the tests to see results here.
Grading and Ask AI run on your own AI account. Your key is stored only in this browser and is sent only to the provider you pick.
Use a capped key. Create a separate key just for this site with a spending limit (an OpenRouter credit limit, an OpenAI project budget, or an Anthropic workspace limit). Browser extensions can read keys stored in a page, so delete the key in your provider's dashboard when you're done.
Unchecked, the key is forgotten when you close this tab.
Kotlin runs on JetBrains' free Kotlin compiler service. Choose how Java runs:
Free and needs no setup. It's shared by everyone, so it can be slow or hit its rate limit.
More reliable, with its own quota. Subscribe to the free Basic plan of Judge0 CE on RapidAPI and paste the key.
Stored only in this browser. Your code is sent to the runner you choose.