Low-level design (LLD) mock interviews

Free LLD mock interviews, with a real engineer

A low-level design round asks you to turn a problem like a parking lot or an LRU cache into classes, interfaces and working code. On Practick you practise it live with another engineer who has the full guide: the scope to agree on, the constraints to hand out, the follow-ups to push on and the code to expect. It is free: interview someone for an hour and you have earned your own.

Book a free mock interview

What happens in an LLD mock interview

You get a short prompt, such as "design a parking lot". You agree on scope, name the main entities and what each is responsible for, sketch the classes and interfaces, and then write the core of it as code. Your interviewer hands out constraints only when you ask for them.

Then the design gets pushed. A new vehicle type, a second payment method, two people booking the same seat at the same moment. A good design absorbs the change by adding a class; a weak one needs rewriting.

What interviewers look for in low-level design

Clear responsibilities: each class does one job, and you can say which
Extensibility: a new requirement means adding code, not rewriting what works
Patterns where they fit: strategy, observer or state to solve a problem you can point to, not everywhere
Concurrency: what happens when two requests reach the same object at once
Working code: the core flow runs, not only a class diagram

LLD and system design are different rounds

System design (HLD) is about services, storage and scale: how millions of users reach a ticket booking system. Low-level design is about the code inside one of those services: the classes that make sure two people never get the same seat. Many companies run both, and practising one does not prepare you for the other.

How to get the most out of each round

Agree on scope first: list the use cases you will support, and the ones you will not
Start from the entities and how they relate before writing any code
Name a pattern only when it solves a problem in front of you
Leave time to walk one full flow end to end

Some of the LLD questions you might get

The bank has 30 low-level design rounds. A few of them:

Design a parking lot
Design an LRU cache
Design Splitwise (expense sharing)
Design a movie ticket booking system
Design an elevator control system
Design a digital wallet with a double-entry ledger

Frequently asked questions

What is an LLD interview?

A round where you design the classes, interfaces and core code for one component, such as a parking lot, an LRU cache or an expense splitter. It tests object oriented design, extensibility and clean code rather than scale.

How do I book an LLD mock interview?

Choose Low-Level Design as the track when you book a slot. Interviews run on Tuesday and Sunday evenings, with slots at 9 PM and 10 PM IST.

Do I need to know design patterns?

Knowing a handful helps: strategy, observer, state and factory cover most rounds. Interviewers care more that you use one to solve a real problem in your design than that you can name many.

Is it free?

Yes. Being interviewed costs one credit, interviewing someone earns one, and new accounts start with one free credit. No card is ever needed.

More ways to practise

DSA mock interviews: Live coding rounds on data structures and algorithms problems.
System design mock interviews: HLD rounds like Design Twitter, Uber and a rate limiter.
SWE mock interviews: Rehearse the technical rounds of a software engineering loop, coding and design.
Free mock interview practice: How Practick stays free, and what you get without paying anything.
Peer mock interviews: Take turns interviewing each other, with a guide for every question.
A Pramp alternative: Free peer to peer mock interviews with a guide for every question.

DSA interview questions · System design interview questions

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