System Design Exercises¶

Going past the checklist

Every exercise ends with a Self-Assessment checklist — good for confirming you covered the material. A few flagship exercises (URL shortener, Rate limiter, Payment processing, WhatsApp) also carry a Five-Level Self-Assessment (Explain → Predict → Diagnose → Design → Defend) — a harder bar than "did I cover it," testing whether you can reason about the design under a new scenario, not just recall it. Apply the same five questions to any other exercise here once you've worked through it: state the core mechanism in one sentence, predict what breaks under a named change in load, diagnose a symptom back to its likely cause, extend the design to a new requirement, and defend your choice against the next-most-obvious alternative.