For SDE-1, SDE-2 and Senior interviews
Load-test your own designs, take AI mock interviews, and get an honest verdict against your target level.
Free to start. Your first Drill takes 7 minutes. Or play Level 1, no sign-up
How slow it gets as users growp95 = the slowest 1 in 20 requests
What is real
See every featurePractise
Start with seven minutes. Move up to a full interview when you are ready.
New every day
One real situation, the same for everyone. Read it here, then start the 7-minute Drill when you are ready. How the Drill works
Next Drill at 05:30 IST
Your fintech app keeps customer balances in an LSM-based key-value store on 3 nodes. It takes only 3,000 writes per second of about 200 bytes, but reading one account sometimes takes 40 ms at p99. Product now wants range reports, joins with transactions and "balance at 5 pm yesterday".
About 7 minutes. 3 to 5 questions, and a short report at the end.
Trains: API and data model, Estimation, Cost and trade-offs
Start today’s DrillHow it works
No slides and no theory first. You build something, break it, and learn why.
Start with the numbers: requests per second, how many are reads, how much data. Small sums, shown step by step.
Choose the parts: load balancer, app servers, cache and database. Set how big each one is.
Add users until something breaks. You see the exact moment, and the part that gave up.
A clear answer against your target level, with the one thing to fix next.
See the simulatorPlay Level 1 free, with no sign-up.
Honest verdicts
The same answer can pass at one level and fall short at the next. You pick your target, and every verdict says which bar it used.
SDE-10–2 yrs
Clear requirements and a working design with the main parts. Rough numbers are enough, and the interviewer can prompt you on the hard parts.
SDE-22–5 yrs
Drives the design from requirements to deep dives, makes estimates, picks parts with reasons, and handles at least one failure without being asked.
Senior5+ yrs
Weighs trade-offs across the whole system, raises failure, consistency and cost without being asked, and reshapes the requirements.
Sample verdict · Design a URL Shortener
Close to the bar
Judged against the SDE-2 bar. You drove the design well; the deep dive on failure needed a prompt.
Judged against: SDE-2 bar. You can change your target level in My Prep.
The whole product
System design has no answer key, so we built a loop. Each page below shows what you get, with no login.
Take in one idea at a time, in plain English.
Use it. Build it, break it, and do it every day.
Take a real round and see an honest verdict.
Pricing
Pay once for a pass. It ends by itself: nothing renews, nothing to cancel.
Founding price
Practice on tap for a whole year, for one payment.
200 of 200 left
One time. Nothing renews.
Recommended
Steady practice for the month before your interview.
One time. Nothing renews.
A few mocks for an interview that is coming up.
One time. Nothing renews.
Every paid plan includes everything in Free, and a mock can be any of the five types: system design, coding, machine coding, resume or simulator interview. Fair use: the AI tutor and Drills share one AI time limit for each pass, and AI mock interviews have their own.
Today’s Drill is ready: “Account reads are slow on a store built for fast writes”. A new one arrives at 05:30 IST.
Try today’s Drill