Prep for your role
System Design Interview
Open-ended design rounds reward a clear process more than memorised architectures. Learn one repeatable structure and you can reason calmly through any prompt.
A system design interview asks you to architect a large system, such as a URL shortener, news feed, or chat app. Interviewers grade your process, not a single right answer: clarify requirements, estimate scale, sketch a high-level design, go deep on one or two components, and discuss bottlenecks and trade-offs out loud.
The repeatable structure
- 1
1. Clarify requirements
Separate functional from non-functional needs. Confirm scope, scale, read vs write ratio, and what 'good' looks like before drawing anything.
- 2
2. Estimate scale
Do rough back-of-envelope numbers: users, requests per second, storage, bandwidth. They drive every later decision.
- 3
3. High-level design
Sketch the major components: clients, API, services, datastores, caches, queues. Show the request flow end to end.
- 4
4. Deep dive
Pick one or two components the interviewer cares about (data model, the hot path, sharding) and go deep with trade-offs.
- 5
5. Bottlenecks & trade-offs
Name the weak points: single points of failure, hot keys, consistency vs availability. Propose mitigations and state what you would monitor.
What interviewers are really grading
- Structure: do you drive the conversation, or wait to be led?
- Trade-offs: every choice has a cost. Naming them is the signal.
- Scale awareness: do your decisions follow from your own estimates?
- Communication: a clear narrative beats a clever but silent design.
Prep for the company you are interviewing with
Design bars vary by company and level. Browse real software-engineering interview loops and sample questions across over a thousand companies.
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How do I prepare for a system design interview?
Learn one repeatable structure (requirements, estimates, high-level design, deep dive, bottlenecks) and practise applying it out loud to classic prompts like a news feed or chat system. The structure matters more than memorising any single architecture.
What do interviewers look for in system design?
They grade your process and communication: whether you clarify requirements, estimate scale, make decisions that follow from those estimates, name trade-offs, and identify bottlenecks. There is rarely one correct answer.
How long is a system design interview?
Usually 45 to 60 minutes. That is not long for a big system, so budget your time: spend the first few minutes on requirements and estimates, then most of it on the high-level design and one deep dive.
How can I practise system design out loud?
Talking through a design is a different skill from reading about one. Rehearse narrating your structure end to end against a timer. A voice mock interview can pose a design prompt and help you hear whether your reasoning stayed clear and structured.
A silent design scores nothing. Practise narrating it.
Run a free voice mock interview and practise talking through a design with a clear, structured narrative.
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