Every system design concept, in motion.
A live wall of the building blocks behind real systems: what each one does, when to reach for it, what bites, and how to talk about it in an interview.
Concepts, grouped by the problem they solve
Each tile runs its own animation. Open one for the plain-language explanation, when to use it, the traps, and an interview prompt with what a strong answer covers.
No concept matches that search. Try a shorter word, like "cache" or "lock".
Ten classic systems, built up step by step
Pick a system. Each step names the concepts you would reach for and why, in the order you would introduce them at a whiteboard.
Problem → reach for
The trade-offs interviewers ask about
Side-by-side tables for the pairs that get confused most often. The last row is the one-line rule of thumb.
How to run a 45-minute design interview
A framework for the hour, the numbers to estimate with, the prompts that come up again and again, quick-fire flashcards, and where to read further.
The 45-minute plan
Time-box each phase. Most candidates spend too long on boxes and never reach the deep dive.
Latency numbers to know
Approximate, log scale. Good enough to tell whether a design is plausible.
Prompts you will be asked
Click a concept to open its tile.
Quick-fire flashcards
Click a card to flip it.
Reference shelf
Where the ideas on this page come from, and where to go deeper.