Find the flaw
Three 5-minute system design challenges
Each one gives you a design with a flaw in it. Say what goes wrong and how you’d fix it, in a few lines. You get real feedback from the grader we use in guided practice, quoting your own words, and one revision. No sign-in needed.
- URL shortenerTake a scam link down in 60 secondsYour short links are cached for 24 h. Support must disable a scam link worldwide within 60 s. How does your design do it?Try it →
- Ticket bookingTwo fans, one last seatLast seat. Two fans click Buy in the same millisecond. Your checkout checks the seat is free, then sells it. What happens and how do you fix it?Try it →
- PaymentsCharged once, even when the app retriesThe payment call times out and the client retries. How do you make sure the customer is charged once?Try it →