Mock system design interview with an interviewer who pushes back
Sketch on the canvas, defend your choices out loud, and get scored on the trade-offs, not the boxes. Forty-five minutes on demand. Your first one is free.
- Twenty prompts: feeds, rate limiters, chat, storage
- Whiteboard canvas plus live voice
- Scored on requirements, design, trade-offs and communication
Built by senior big tech engineers
How the session runs
- 01
Pick the level
Junior, mid/senior or staff, and a target company if you have one. The setup hands you a prompt from the library: a news feed, a URL shortener, a rate limiter, a chat service. Or open any of the 20 prompts in the design library and start the interview from there.
- 02
Design on the whiteboard while you talk
Draw the architecture on the canvas and narrate it. The interviewer interrupts the way a real one does: why a queue there, what happens when the cache dies, how does this shard.
- 03
Get scored on the parts that decide the round
Requirements gathering, design quality, trade-off analysis and communication, each scored from 1 to 5, with the places where you hand-waved called out.
What the interviewer does that a guide can't
- Asks for the numbers: how many writes a second, how big is a row, what does a day of data weigh.
- Picks the component you were vaguest about and makes you go deeper on it.
- Pushes on the requirement you skipped and watches what you keep.
- Doesn't let a box stand without a reason. Every arrow gets asked why.
What you walk away with
- A scored evaluation across requirements gathering, design quality, trade-off analysis and communication, with a verdict from strong hire to no hire.
- Your whiteboard, saved as you left it, next to the evaluation.
- Focus areas from the evaluation, and a recommended next interview at the level the score says you are ready for.
First interview free. Unlimited from $9.99/mo on the yearly plan, or $24.99 month to month. See pricing
What people say after a mock
“The follow up questions were simply amazing. Overall an ultra realistic interview experience, thank you.”
Mohan M · Prepping for Amazon
“This tool is pretty great for someone like me. I have always been intimidated by tech interviews. Even the thought of a failed mock interview and the embarrassment I would feel after giving them had me avoiding them. This tool has helped me realise that I do suck, but I could be a lot worse, I am progressing and feeling more confident as time goes on, and that talking through my process is just as important as the solution, if not more.”
Sirat B · Prepping for NVIDIA
“I can 100% see this being a staple in every software engineer's interview prep process.”
Baid B · Apple Senior SWE
“It was like a real one, the questions, the tone everything.”
Presha M · New Grad
Questions before you start
Prepare for the mock, then come back
- Free system design courses
Caching, load balancing, database scaling, consistency and message queues, each with simulations.
- System design concepts
Start with caching, the block most prompts test, and follow the links to the rest.
- Design library
All 20 prompts with written AI feedback, and the place to start a mock on a specific one.
- How this compares
Guides, peer mocks, coaches and AI interviewers, side by side.