The LLD Interview Framework
Beginner · 14 min read · Low-Level Design, Foundations
How design and machine-coding rounds are run and scored, and a repeatable approach.
Low-level design (LLD) interviews test whether you can turn a problem into well-structured, working, extensible code. Where HLD is about boxes and arrows between services, LLD is about classes, interfaces, responsibilities and the interactions between objects inside one service.
There are two common formats, and preparing for the wrong one is a classic mistake.
The two formats
How much code is enough?
Less than most people fear. The case studies on this site include a full reference design (often 200–350 lines) so you can learn every edge case. Nobody types that in one round. What interviewers actually expect:
What interviewers score
The framework
LLD prompts are as vague as HLD ones. "Design a parking lot" could mean one floor or a multi-storey garage with EV charging, monthly passes and payment kiosks.
Code-quality checklist for the round
Interview questions
- How do you decide what should be an interface versus a concrete class?
- You have 90 minutes for a machine-coding round. How do you allocate time?
- What is noun–verb analysis and what are its limits?
Further reading
Key takeaways
- Clarify whether the round wants a design or working code.
- Requirements → entities → class diagram with interfaces → flows → implementation → extensions.
- Put interfaces exactly where requirements vary; keep everything else simple.
- In machine coding, a working, well-structured core beats an ambitious, half-finished design.
- Expect a twist; good abstractions let you absorb it by adding a class.