Free and open source

Prepare for your backend interview.

Practise every round in Java and Kotlin: code review, coding, debugging, concepts and system design. Earn points and skill badges as you go. Code runs against real tests, and an AI on your own account can grade your work.

Start practising Follow the interview kit

Interview preparation kit

Backend interview kit

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Skills

Earn a badge for every skill.

Each skill collects exercises across all modes. Points add up to stars: one for every 20% of a skill's points.

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Challenges

All challenges

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Bring your own AI

Grading and Ask AI on your own account.

Connect OpenRouter, Anthropic, OpenAI or Gemini. Your key stays in your browser and requests go straight to your provider. There's no server in between, and the free keyword check works without any AI.

Connect on the practice page Add an exercise