System design mock interviews
A system design round has no right answer, which is exactly what makes it hard to prepare for alone. The score comes from how you narrow an open question and which trade-offs you make on purpose.
Rounds with Sia from ₹49 · Live interviews with a working engineer from ₹500 · Pay per session
What a System design round covers
Scoping the question
Turning "design X" into something answerable: who uses it, how much, and what you are explicitly not building. Candidates who skip this end up designing the wrong system well.
Data model and access patterns
What you store, how it is read, and which access pattern drives the choice. Storage decisions made before the read pattern is known are the usual first wrong turn.
Scaling and bottlenecks
Where it breaks first as traffic grows, and what you would measure to know. Naming the bottleneck before adding a cache is the difference between reasoning and pattern-matching.
Trade-offs and failure
Consistency against availability, what degrades when a component fails, and what you chose to accept. This is where senior candidates separate themselves.
System design interview questions you might be asked
Not a list to memorise. Each is the kind of opening a real round uses, with what a strong answer covers — the follow-ups depend on what you say.
Design a URL shortener. What do you ask before you draw anything?
Scope first: how many links, how many reads per write, custom links or not, and whether links expire. The design follows from those answers.
Your notification service has to send ten times more messages next month. What breaks first?
The bottleneck named before the fix, how you would measure it, and why a queue helps here specifically.
Should the feed be built when someone posts, or when someone opens the app?
Write-time against read-time work, which one the usage pattern favours, and what happens for an account with millions of followers.
The cache goes down. What does the user see?
What degrades and what keeps working, how the database survives the sudden load, and what you chose to accept.
Would you use SQL or NoSQL for this, and why?
A choice tied to the access pattern and the consistency it needs — never a choice made by habit — and the alternative you rejected.
Answer questions like these in a scored round and see exactly where your answer fell short.
What the interviewer is listening for
The strongest signal is deliberate narrowing: stating what you are optimising for, then designing for it. Reciting a reference architecture without connecting it to the requirements reads as memorisation and is followed up hard.
Where candidates lose marks
- Jumping to boxes and arrows before agreeing what the system must do.
- Adding a cache, a queue and a shard without saying what each solves.
- Presenting one design as correct and never naming the alternative you rejected.
Two ways to interview
A round with Sia, on your own
One question at a time with real follow-ups on what you actually said. Choose three, five or eight questions. Scored the moment you finish, with a written breakdown across technical depth, problem solving and communication.
A live interview with an engineer
Forty minutes over Zoom with someone who runs system design interviews for a living. They score five criteria and write up what to fix, and you keep a numbered certificate for the session.
Questions about system design interviews
Is system design only for senior candidates?
No. Freshers are increasingly given a smaller design question. Beginner difficulty keeps the round to scoping, a data model and one or two trade-offs.
Is there a right answer?
No, which is why this round is hard to prepare for alone. You are scored on how you narrow the question and which trade-offs you make on purpose.
Should I take this round with Sia or with a live engineer?
Both work. A round with Sia is cheaper for repetition; a live engineer can push back on a design the way a real panel would.
How is a system design round scored?
On the same five criteria as every round, with technical depth and problem solving carrying the most weight, and a written breakdown of what to fix.
Read before your round
Other tracks
Not sure which to book? The FAQ covers how sessions are scored, and candidate stories show what people did with the feedback.