Design Method & StylesChapter 15 · Open the room
Interview & rubric
Interview & rubric
A system design interview is a 45-minute conversation in which you design a system out loud with an interviewer. There is no answer key. You're scored on how you get there — scoping the problem, estimating its size, shaping an architecture, going deep where it matters, defending trade-offs, and communicating the whole way. Split the minutes across those phases, steer the conversation yourself, and say your reasoning as you go.
- Use when
- Preparing for a system design round, usually asked of mid-level and senior engineers · Practicing any case on this site in interview mode — the debrief scores the same six dimensions · A design review where you have one short meeting with the people who decide
- Avoid when
- As a template for real design work — a real design has weeks, data and many stakeholders, not 45 minutes and one listener · Reciting a memorized design for a famous prompt — the score is for reasoning about this prompt's requirements
- Trade-offs
- Covering every phase versus going deep in one — skipping estimation buys deep-dive minutes but leaves the design unanchored · More clarifying questions sharpen the scope and eat the clock · Naming what a choice costs takes one sentence and is worth more than an extra component you can't justify
3 objectives · 5 misconceptions
- explain Explain the six things a design interview scores — scoping, estimation, architecture, deep dive, trade-offs, communication — and which phase of the 45 minutes gives the interviewer evidence for each.
- choose Choose how to split 45 minutes across clarify, estimate, API, high-level design, deep dive and trade-offs, and when to cut a phase short to protect the deep dive.
- predict Predict how two different designs for the same prompt would score — by the requirements each meets and the trade-offs you name out loud, not by how close each is to a reference answer.
- Not true: There is one correct design, and the interviewer is checking whether you find it.
- Not true: Strong candidates start drawing boxes in the first minute to show speed.
- Not true: More components — more caches, queues and services — earn a higher score.
- Not true: Working quietly and presenting a finished answer looks more confident than thinking aloud.
- Not true: The interviewer leads; your job is to answer the questions they ask.
Practice
No katas practise this yet.