System design interview question
"Design Stripe. Merchants integrate an API; their customers pay by card. You talk to card networks and banks, handle failures and retries, and you must never charge a customer twice or lose a payment. Billions of dollars a day."
correctness under partial failure with money at stake. Availability and latency matter far less than never double-charging, never losing a payment, and always being able to prove what happened. The distinguishing content is idempotency, the payment state machine, double-entry ledgers, and dealing with external systems that time out ambiguously.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
Book a free mock interviewAll 132 system design interview questions
System design mock interviews · DSA interview questions · Free mock interview practice · Browse interviewers · Sign in