System design interview practice

Practice a system design interview with a model acting as interviewer, pushing back the way a real one would instead of just agreeing.

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Fill in the variables

Act as a system design interviewer for a {{experience_level}} role. The
prompt is: "{{prompt_topic}}".

Rules for how you run this:
- Don't give away the "ideal" design. Ask clarifying questions the way a
  real interviewer would (scale, read/write ratio, consistency
  requirements, latency budget) and wait for my answers before letting me
  proceed.
- When I propose a design, push back on the weakest part of it -
  a bottleneck I didn't address, a failure mode I didn't consider, a
  tradeoff I asserted without justifying - the way a real interviewer
  would probe rather than accept it.
- If I go quiet on a topic (never mention data consistency, never mention
  failure handling), prompt me on it specifically rather than letting the
  session end without covering it.
- After the session, give me feedback structured as: what I covered well,
  what a strong candidate at this level would have covered that I missed,
  and one specific thing to practice before the next attempt.

Start by asking me your first clarifying question.

When to use

Practicing for an upcoming system design interview, especially to rehearse handling follow-up pressure rather than just rehearsing a memorized design. Also useful solo, without a study partner, since the “don’t give away the answer” instruction is what makes it feel like a real interview instead of a tutorial.

Why it works

The easiest way to fail a system design interview isn’t a wrong initial design - it’s freezing or hand-waving when the interviewer pushes on a weak point. Rehearsing that specific moment (being challenged, having to justify a tradeoff on the spot) matters more than rehearsing the “correct” design, which is why the instructions explicitly forbid the model from just handing over the ideal answer.

Variations

Add “This is a follow-up round - assume I already covered the basic design in a previous round, focus on deep-diving one component” for senior-level practice.
Ask for the feedback in the format your actual interview loop uses (a rubric, a hire/no-hire recommendation with reasoning) if you know it.
Run it twice on the same prompt a week apart and compare the feedback - improvement (or its absence) is more useful signal than any single session’s score.