How to approach a system design question
By the end of today you have a repeatable method for any design question, and you can resist the urge to name technologies before you have established what the system must actually do.
YesterdayPhase 5 made one service operable. Phase 6 asks what happens when one machine is not enough.
TomorrowTomorrow you put numbers on it, because a design without estimates is just a diagram.
Why this matters
System design has no single correct answer, which is exactly why a method matters. Without one, people list technologies they have heard of and cannot defend any of it.
- The design method
- Functional requirements
- Non-functional requirements
- Cutting scope
Learn it
75 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
5 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
50 minTake a design question of your choice, such as a pastebin or a rate limiter, and work through the method in writing without naming a single technology until the final step. Then write down what would have to be true before you would add a cache, a queue, or a second database.
Recall it
20 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
5 recall questions
Free · sign inQuestions you answer from memory, then grade yourself against the real answer. The score is carried into the mastery rating below it, so an honest miss cannot quietly become a tick.
Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
Free · sign inRate yourself against five named criteria per concept. Completion and mastery are tracked separately, and anything you rate shakily comes back automatically on a spaced schedule.
Recap
- 01The question tests reasoning under uncertainty, not memorised architectures
- 02Requirements first, because everything after depends on them
- 03The simplest thing that could work is usually the right first answer
- 04Find the bottleneck, fix only that, and repeat
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.