System Design Round
One open-ended prompt in 45 to 60 minutes, with follow-up questions on scale and failure. You lead the discussion: requirements, estimates, API, a high-level design, and two deep dives.
Start a Session
Set a level to tune the cards. Cards you rated Shaky come up more often.
How It's Graded at Each Level
- Junior
Rarely asked. When it is, a working sketch and a clear API carry it.
- Mid
A sound high-level design, basic scaling, and one tradeoff you can defend.
- Senior
You drive. Estimates come first, and two deep dives cover failure modes and hot spots.
- Staff
You frame the problem, name what not to build, and plan the migration across teams.
- Principal
Multi-year evolution, org-level risk, and build versus buy at company scale.
Drill Types
Read These First
All System Design Pages- WalkthroughDesign TinyURLWalkthrough
- WalkthroughDesign a Distributed Rate LimiterWalkthrough
- TechniqueIdempotency KeysTechnique
- TechniqueExponential Backoff and JitterTechnique
- TradeoffKafka Versus SQSTradeoff
- TradeoffConsistent Hashing Versus Mod NTradeoff
Common Mistakes
Drawing boxes before requirements
Five minutes of scoping saves twenty minutes of redesign.
Estimating after the design
Read to write ratio and storage should shape the boxes.
One database with no reason given
Name the access pattern, then pick the store.
Deep diving on the comfortable part
Spend the time where it breaks: hot keys, failover, and backpressure.
Matching Mock
Interview Simulator
A 45 minute round, phase by phase, with interviewer follow-ups, a checklist for your level, and a report at the end.