# Final Design Interview Checklist — High-Level & Low-Level Design Interview Problems

Source: https://www.skillbyai.com/en/design-interviews/final-checklist

> Review before and during the round.

## What to cover every time

Before you finish, make sure you have: clarified functional and non-functional requirements; stated assumptions and rough numbers, clearly labelled as assumptions; identified core entities and APIs or classes and interfaces; drawn a clear diagram and walked a use case through it; deep-dived into the hardest part; addressed consistency, concurrency and idempotency where money, inventory or shared state is involved; discussed scaling, bottlenecks and failure modes; named trade-offs and alternatives; and summarised the design and possible extensions in the last minute.

## The checklist

Keep it beside you when practising.

```text
[ ] requirements clarified; scope agreed; out-of-scope stated
[ ] assumptions + rough estimates labelled as assumptions
[ ] HLD: entities, APIs, data model   |  LLD: classes, interfaces, relationships
[ ] diagram with labelled flows        |  class diagram with multiplicities
[ ] one use case walked end to end
[ ] deep dive on the hardest component
[ ] consistency, concurrency, idempotency where shared state or money
[ ] scaling: partitioning, caching, replication, async work
[ ] failure modes: timeouts, retries, failover, degradation
[ ] trade-offs and rejected alternatives explained
[ ] LLD code: readable names, small methods, edge cases handled
[ ] 1-minute summary + extensions
```

## End with a summary

A crisp one-minute recap of requirements, design and key trade-offs leaves the interviewer with a clear picture of your reasoning.

**Quiz:** Which belongs on a design interview checklist?

- [ ] Avoiding any mention of failures
- [ ] Skipping requirements to save time
- [x] Labelling estimates as assumptions and explaining trade-offs
- [ ] Using every design pattern you know

*Answer:* Labelling estimates as assumptions and explaining trade-offs. Structure, honesty and judgement.