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.

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.

Practice thinking out loud

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.

Browse engineering interview guides by company

System design FAQ

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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System Design Interview

The repeatable structure

1. Clarify requirements

2. Estimate scale

3. High-level design

4. Deep dive

5. Bottlenecks & trade-offs

What interviewers are really grading

Prep for the company you are interviewing with

System design FAQ

A silent design scores nothing. Practise narrating it.

You've got the resume. Now build the stories that back it up.