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System Design Interview: Core Concepts
Defend a system design out loud under a timer, naming the trade-off an interviewer is grading instead of listing components. For developers who already run production systems and need the vocabulary at hand, not taught from zero. Ninety-six cards in eleven chapters, from scoping the requirements through caching, replication, partitioning, queues and model serving; it drills the room, not algorithms or vendor products.
'Design Twitter.' The interviewer stops talking. What is your first move, before a single box is drawn?
Agree the scope out loud: who the users are, the two or three things the system must do, and the scale it runs at. The design is scored against the requirements you name here.
— The first artefact is a list, not a diagram.
Source
Requirements work is the most common written feedback at mid-level and stays top-three at senior (Hello Interview, 'system design requirements'). The ritual is short: functional requirements first (what a user can do), then the non-functional ones that shape the architecture, then the scale. Two or three functional requirements is the right number for forty-five minutes, and saying 'those are the ones I will design for' invites the interviewer to correct you while it is still cheap. Drawing first is the losing move: every box you cannot justify from a requirement is a box you will defend for free.