Why system design is my favorite interview

System design is presented as the highest-signal interview format for evaluating engineers. The post says good interview design correlates strongly with on-the-job performance, and that system design shows how candidates think, ask questions, and make tradeoffs in a way leetcode does not.

Reading notes

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• The format is described as the opposite of a leetcode interview, with open-ended discussion, many questions, strong opinions, and no single correct answer.
• The interviewer keeps introductions short so the candidate has more time, and leaves time at the end for questions.
• A typical prompt includes a problem statement and scale numbers, because designing for 100 users is different from designing for 1 billion.
• The suggested order is data schema, API, data querying, then hosted architecture.
• The interviewer says to hand-wave parts of the system with phrases like “Let’s assume that part is implemented” so the candidate can focus on the part being solved.
• The post says people get better at system design with experience, unlike leetcode, so the interview highlights what candidates have done rather than what they have read.
• A key check is whether the candidate builds an appropriate system for the given scale or over-designs with the biggest system they know.
• Another check is whether they can explain the pitfalls of choices like sharding or caching, including invalidation.
• The interviewer looks for candidates who ask business questions, accept engineering suggestions, admit when they do not know something, and adjust their design accordingly.
• Strong candidates present multiple options, discuss pros and cons, ask a few questions about the broader system, choose one option, and explain how the design changes as the system evolves.
• The post frames system design as a useful leveling interview because it reveals whether someone is fresh or experienced, along with their blind spots and strengths.