Practice system design the way the interview actually goes
Every question is a guided 45-minute run: scope the requirements, do the numbers, draw the design, walk the user flows on a live diagram, then defend your choices against the follow-ups an interviewer asks next. Study mode shows everything. Practice mode hides every answer until you have produced your own.
No sign-in needed for the free question. Pro from $79 a year.
Amazon
ShopifyQuestions
Each one teaches patterns the others do not. Design a URL Shortener is free, in both modes; the rest are Pro.
Design a URL Shortener
bit.ly at scale: turn long URLs into short codes, redirect in milliseconds from anywhere, count the clicks.
Design Slack
Real-time team messaging: channels, DMs, presence, history and search for millions of concurrent users.
Design a Payment System
Accept card payments for an e-commerce platform, move money correctly exactly once, and be able to prove it.
Design a News Feed
The home timeline of Twitter, Instagram or Facebook: posts from people you follow, ranked, fresh, and fast for hundreds of millions of users.
Design YouTube
Upload, transcode, and stream video to a billion viewers: a processing pipeline on one side, a CDN problem on the other.
Design Google Maps
Map tiles, place search, turn-by-turn routing with live traffic, and ETAs for a billion users.
Design a Matchmaking System
Group online game players into fair, low-latency matches within seconds, at millions of concurrent players.
Design Uber
Match riders with nearby drivers in seconds, track trips live, and price them, for millions of concurrent users worldwide.
Design a Notification System
Deliver push, email, SMS and in-app notifications to hundreds of millions of users: the right channel, once, on time, and never at 3 a.m.
Design a Web Crawler
Fetch billions of pages a month politely, discover new links, skip duplicates, and keep the copy fresh without getting the crawler banned.
How a question works
Five screens in the order an interview runs. In practice mode each must be finished before the next unlocks.
- 01
Scope the requirements
Functional requirements with the constraint that makes each one interesting, an explicit out-of-scope list, and non-functional targets with real numbers.
- 02
Do the numbers
Back-of-envelope estimates with the arithmetic shown. In practice mode you type each number and are graded against the derivation.
- 03
Draw the design
An interactive high-level design. Click any component for what it does, what backs it, and the non-obvious decision inside it.
- 04
Walk the flows
Five user flows per question: the happy path, the read path, the scale-breaking case, a failure or retry, and a background job. Each step lights up the components and calls, with an API sketch.
- 05
Defend the choices
Deep dives compare three or four realistic alternatives, pick one with concrete keys, thresholds and TTLs, then ask the follow-ups an interviewer asks next.
Everything visible. Flows can autoplay across the diagram. Read a question end to end in about 40 minutes, the night before.
Every answer hidden until you ask. Type the estimates, click the components a step touches, press Check, and see what you missed. A session timer counts only active time.
Study guides
The theory behind the questions: one page per building block, written to be said out loud in an interview. Free to read.
Pricing
One product, three ways to pay. Every plan unlocks every question, including the ones added after you buy.
Monthly
Cancel any time. Good for a focused interview loop.
Annual
Less than two months of monthly. For an ongoing prep habit.
Lifetime
Three years of annual, paid once. Keep every question added later.
Payments by Stripe. Cancel subscriptions any time from the billing portal; 14-day refund on a first purchase. Full details.
Questions people ask
How is this different from reading a system design book or blog?
Reading tells you the answer. Practice mode makes you produce it: you scope requirements before seeing ours, type each estimate and get graded, click the components a step touches on a live diagram and get corrected, and answer interviewer follow-ups before the model answer opens. That is the difference between recognising a design and being able to say it out loud under pressure.
What is in a question?
Five screens, in the order an interview runs: functional requirements with explicit scoping, non-functional requirements with numeric targets, back-of-envelope estimates with the arithmetic shown, a high-level design diagram with five user flows that light up the components and calls of each step (with API sketches), and five or six deep dives that compare realistic alternatives, pick one, and then ask the follow-up questions an interviewer asks next.
Which questions are free?
Design a URL Shortener is open to everyone, in both study and practice mode, with no sign-in. It is the whole product, not a teaser: try it before deciding on Pro.
What does Pro include?
Every question on the site, every question added later, practice mode on all of them, and your session history synced across devices when you sign in. All three plans include the same content; they differ only in how you pay.
Does the subscription renew automatically?
Monthly and annual plans renew until you cancel. Cancel from the billing portal at any time and you keep access until the end of the period you paid for. Lifetime is a single payment with no renewal.
Can I upgrade from monthly to annual or lifetime?
Yes. Open the billing portal from the pricing page and switch plans; Stripe prorates the unused part of the current period.
Is there a refund policy?
If Pro is not what you expected, email within 14 days of your first purchase and it is refunded. Renewals are not refundable, so cancel before the renewal date if you are done.
Do I need an account?
Not for the free question. Signing in with Google is required to buy Pro and to sync study history across devices. Without an account, your progress lives in your browser.
Where do the "asked at" company logos come from?
Public interview guides and candidate reports. They indicate where a question has been reported, not a verified dataset, and a company name never implies endorsement.
What level is this for?
Senior and staff loops at large tech companies, where the interview is 45 to 60 minutes, expects numbers, and spends most of its time on deep dives. Mid-level candidates use it too; the study mode reads as a complete walkthrough.