Mock Interview

System design

Structured reasoning about scale, tradeoffs, and bottlenecks.

Mock mode

Overview

The system design interview tests whether you can architect a scalable system from ambiguous requirements — scoping, estimating load, and reasoning about tradeoffs across components. It's about structured thinking, not memorized diagrams.

How it works

Mock mode

ClientServiceEdgeData

Step by step, with examples

1
Requirements
- Functional, non-functional, and scale.
2
High-level
- Boxes: LB, service, DB, cache.
3
Bottlenecks
- Sharding, caching, and queues.
4
Trade-offs
- Justify your decisions.
- Example: CAP theorem

What it tests

Structured reasoning about scale, tradeoffs, and bottlenecks.

Format & timing

45–60 min · open-ended design on a whiteboard.

Sample questions

Design a URL shortener that handles 100M reads/day.
Design a news feed for 300M users.
Design a rate limiter for a public API.

Model-answer walkthrough

Clarify functional + non-functional requirements.
Estimate scale (QPS, storage, bandwidth) out loud.
Sketch the high-level design and the API.
Detail the data model, then scale with cache/queue/sharding.
Call out bottlenecks and the tradeoffs you accept.

What good looks like

Drives the conversation
Quantified capacity estimates
Sensible component choices
Explicit tradeoffs and bottlenecks

Likely follow-ups

What breaks at 10× traffic?
How do you keep it consistent?
Where's the single point of failure?

Common mistakes

Jumping to components before requirements
No numbers
Ignoring failure modes
Over-engineering early

Pre-round checklist

Memorize a staged framework
Practice capacity math
Prepare 3–4 canonical designs cold

Where this content comes from

For full transparency, this content is curated and verified from these sources:

AI-generated, role & company-aware questionsReported interview formats by companyCalibrated against real interview rubrics