“Okay, I'll start with the part that matters most, which is somebody clicking a short link. So there's a browser. It asks for our domain, slash, the code…”
Practice for system design interviews
Think it through. Out loud.
A system design interview with a voice interviewer that follows your reasoning, not a script. Sketch on a shared canvas, pause for coaching when you're stuck, and read a Report against the bar for your level.
Private beta · one free session when you're in
Design a URL shortener
InterviewerSpeaking15:25
“Back to your 301. The same person clicks that link a second time: what does their browser do, and what does your service see?”
The code got automated. The thinking is yours.
What stays yours is judgment: deciding what to build and why, weighing the trade-offs, and explaining a design out loud when someone pushes back.
Think Aloud is where you practise it, as often as you need. It is practice, never help during a real interview.
It follows you
Start wherever you like. The next question comes from what you just said.
Nothing is read from a script. Two Candidates got the same brief and opened differently, and the interviewer followed each one.
The brief both Candidates heard“Design a URL shortener. Someone pastes a long link and gets a short one back; anyone who opens the short link lands on the original page.”
“Before I draw anything, can I pin down what's in and out? … A hundred million over eighty-six thousand, about twelve hundred a second.”
1,200 links/s115k redirects/s230k at peak
Thirty minutes, one real interview.
A desktop browser and a microphone. 30 or 45 minutes.- The brief
- You talk and sketchafter the interviewer reads the brief
- Coachingif you pause
- Back to the interviewsame canvas, same clock
- You wrap upthe last four minutes
Your Reporta few minutes later
Talk it through
Ask for numbers, weigh the trade-offs, change your mind out loud. The interviewer hears you and asks about the part you skipped.
Sketch as you go
A shared canvas the interviewer reads while you draw. It can point at a box you made and ask what happens there.
Read your Report
What you showed against the bar for your level, each point with the words you said.
Coaching
Stuck? Pause. Learn it. Pick up where you left off.
Pause mid-interview and a coach walks you through the part you're missing. Then you go back to the same interviewer, the same canvas, and the clock. Pauses can use up to a fifth of your time.
Interview pausedCoaching · 5:58 left
Coach
“You already said every click goes to the database. Don't stop at slower: think about how much the database was sized for, and what it gets in that minute.”
Report · Attempt 1 · Mid barDesign a URL shortener
Framed before designingShown
Sized with numbersShown
Laid out both paths end to endShown
Chose the record, its key and the callsShown
Separated the redirect path from creationShown
Designed for failurePartly
Owned trade-offsShown
Explained how the mechanism worksShown
Canvas qualityShown
Sized with numbersShown
Met
Does arithmetic out loud from a given or assumed number to a new figure the interviewer did not read out, and says its unit.
“Redirects, ten billion over eighty-six thousand, roughly a hundred and fifteen thousand a second.”In context
The Report
No score. No verdict. Your own words, against a written bar.
Every point quotes what you said, and one click shows the moment you said it. What the interview never reached is marked as not judged, not held against you.
Interviews you can practise today
System design · 30 min · Junior to Senior
Design a URL shortener
Someone pastes a long link and gets a short one back; anyone who opens the short link lands on the original page.
System design · 30 or 45 min · every levelDesign a chat app
People send text messages to each other from a phone or a laptop.
System design · 30 or 45 min · Mid to StaffDesign a ticketing system
Design a ticketing system for concerts and shows.
System design · 30 or 45 min · Mid to StaffDesign a video platform
People upload a video from a phone or a laptop, and anyone can watch it — on a slow connection, on a TV, anywhere in the world.
Pricing
One price per session, however long you think.
One session is one whole interview.
You pay for the interview, never the minutes, so take the time a real answer needs.
- 30 or 45 minutes
- You choose the length. The price is the same.
- A live interviewer
- It follows your design on a shared canvas.
- A written Report
- Judged at your Level, quoting what you said.
One-time payment, no subscription. Sessions never expire. Prices in USD, tax included.
First sessionwith your inviteFree
1 Sessionone interview$8
5 SessionsSave $10$6 a session$30
Private beta · one free session when you're in
Questions
- Will it understand my accent?
- It transcribes what it hears, and your Report quotes you word for word so you can check it. The Report judges what you reason and draw, not how you sound.
- Is my voice recorded?
- No. Your voice reaches the interviewer while the session runs and isn't kept. The transcript and your canvas are kept to write your Report, and only you can open them. Privacy Policy
- How is it different from a mock with a person?
- A person brings judgment of their own. Think Aloud brings the repetition: the same written bar every time, any evening, as often as you need.
- Can I use it during a real interview?
- No. It's a place to practise, and nothing in it listens in on a real interview.
- What do I need?
- A desktop browser and a microphone. Sessions last 30 or 45 minutes, and your Reports read fine on a phone.
- Can my company use it?
- Not yet. An assessment mode is on the way: the same interview, with coaching off and the Report sent to the employer.
Practise the part that's yours.
Start with the URL shortener. Thirty minutes, out loud.
Private beta · one free session when you're in