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AI system design mock interview
Practise the system design interview against an AI interviewer that runs it the way a real one goes: a one-line brief, six phases, questions both ways, and a review at the end that names what to fix first.
How it runs
You get a one-line brief, such as "design a chat system". The interview takes an hour to type, the length of a 45-minute spoken interview stretched for typing, in six phases:
- Requirements (7 minutes)
- Estimates (7 minutes)
- API and data model (7 minutes)
- High-level design (13 minutes)
- Deep dives (20 minutes)
- Wrap-up (6 minutes)
The interviewer answers the questions you ask it, asks its own, and pushes on what you leave vague. You keep notes for each phase and build the design in the simulator, so the design is something you can run under load, not only describe.
Pick your level
You say whether you are aiming for a junior, mid-level or senior role, and the interview holds you to it.
- Junior: a design that works end to end, with a reason for each part. The deep dives stay on the basics: correctness on one store, safe retries, caching.
- Mid-level: a sound design with its main trade-offs named. The deep dives add the patterns that span machines, and what each one costs.
- Senior and above: you drive it, naming trade-offs and failure modes without being asked, backed by numbers. The deep dives add skew, outside systems and more than one region.
The review
When time is up you get a review against a strong answer for your level. It names the biggest fix first, quotes the evidence from your own interview, and lists what a strong answer would have added. You can then retry the dive you handled worst.
Before you start
The lessons are free and work without an account. The AI interviewer needs a free sign-in with GitHub, and each account has an allowance of mock interviews, since every one has a running cost. Mock interviews on paper, which have no AI, are free without signing in.
Each chapter ends with a problem in the simulator, and the mocks assume you have met the building blocks, so the best order is to start learning and then open interview practice.