Capital One System Design Questions

Design a geography-aware virtual card service

Design a virtual credit card service for a bank: customers generate virtual card numbers (single-use, merchant-locked, or with spending limits, possibly geography-aware) linked to their real account. On each transaction the…

Also reported as: Validate virtual credit card transactions from encoded IDs

Design Credit-Card Authorization, Limit Decisions, and Reporting

Design a credit card system that supports application login, real-time payment authorization with fraud detection, credit-limit decisions (approve or deny based on available credit), a view of the user's spending, and monthly…

Design a credit card portal

Design a credit card customer portal: users log in, view card details, balance, available credit and statements, see transactions, make payments, set alerts, and manage their card (lock/unlock, replace). Discuss authentication…

Design a mobile banking app backend

Design a secure, highly available backend for a mobile banking app: accounts and balances, transaction history, transfers and bill payments, notifications, and customer profile. Discuss API and service design, the data model…

Design a highly reliable account balance system

Design a highly reliable backend service that stores and updates user account balances (a wallet or bank ledger). Support deposit, withdraw, transfer between accounts, and balance/history queries. Requirements: balances are never…

Design a cross-region event processing platform

Design a cross-region event processing platform: producers in multiple regions send events continuously; the platform stores them durably and delivers them to multiple consumer groups for processing. Requirements: no data loss if…

Threaded replies in a chat app (Slack/Teams)

Design a real-time chat system like WhatsApp or Slack supporting one-to-one and group conversations (and, for Slack variants, workspaces, channels and threaded replies). Users send and receive messages with low latency, see…