Stripe
stripe
System Design
Design a Payment System (Stripe)
Design a Stripe-style payment platform that processes 100M payments per day across 50 currencies and dozens of payment methods, where the central requirement is financial correctness: never charge a customer twice, never lose a payment, always reconcile to the cent. The interview centerpiece is the trio of idempotency keys, the payment intent state machine, and the immutable double-entry ledger - together they make the system safe in the face of network failures, partial outages, and adversarial retries. We also cover webhook delivery with signing and exponential backoff, PCI scope minimization through tokenization, multi-region availability, and the reconciliation jobs that compare our ledger to the bank's settlement files every night.
Community
System Design Interview at Stripe
A senior backend system design round at Stripe centered on idempotent webhooks, the failure mode I missed, and how the interviewer pushed me from a clean diagram to a defensible one.
The Stripe Loop Questions I Actually Got
A 5-question reconstruction of a senior backend loop at a payments company in 2024. Each one is paired with what the interviewer pushed back on and what I should have answered.
Idempotency Keys: The Pattern Stripe Taught Everyone
The key itself is the trivial part. The lifecycle, the storage, the body fingerprint, and the TTL are where production teams trip.