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FollowtheDamnCode

A tutor that asks the next question instead of handing you the answer.

Practice data structures, system design and AI/ML for interviews with a coach that makes you do the thinking. It runs on your own computer, and your code never leaves it.

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Mac and Windows. Free to start, no card needed.

two_sum.pyPython
1def twoSum(nums, target):
2    for i in range(len(nums)):
3        for j in range(i + 1, len(nums)):
4            if nums[i] + nums[j] == target:
5                return [i, j]

Coach The loop on line 3 runs once for every i. With ten thousand numbers, roughly how many pairs is that? And what would you have to already know to skip it?

You About fifty million. I'd need to remember the numbers I've already seen?

Coach Yes. What could you keep them in, so that finding one doesn't cost another loop?

An example exchange. The coach never writes your solution.

How every problem goes

The same six stages each time. You move on when you can explain your answer, not when you have pasted one.

  1. 1UnderstandRestate the problem in your own words and pin down what it really asks.
  2. 2IntuitionNotice the obvious first move, and start wondering if there is a smarter one.
  3. 3Brute forceWrite the simple version and say what it costs.
  4. 4TradeoffsFind the bottleneck and decide what you would trade to remove it.
  5. 5OptimizeArrive at the better solution yourself, with the coach asking rather than telling.
  6. 6FinalState the complexity and defend why your answer is correct.

What you can practise

Data structures and algorithms
34 topics from complexity to dynamic programming, each with lessons, animations and coached problems.
System design
The fundamentals (networking, caching, databases, queues) and worked case studies, with animated walkthroughs.
AI and ML
From what an LLM is to RAG and agents, plus the maths and the ML concepts that come up in interviews.
C and Python from zero
Two full beginner courses with exercises that run and check your code on the spot.
Design patterns and low-level design
SOLID, the 23 patterns, code smells, refactoring and LLD practice.

311 coached problems across the tracks.

Built to run on your machine

Your code stays on your computer

Solutions, coach conversations and progress are stored on your machine. Our server holds only your account: email and plan.

A coach that runs where you do

Use a model that runs on your computer, or bring your own Anthropic or OpenAI key. Your key is sent only to that provider.

Works offline

After you sign in, the app keeps working without internet for up to 7 days before it asks you to reconnect.

Real tests in 6 languages

Python, JavaScript, Java, C++, C, Swift. Your code runs against hidden tests, the way an interview platform runs it.

Start with the free topics

The C and Python courses, the first three DSA topics, and the opening lessons in system design and AI are free, with the full coach.

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