Design
Fraud Detection System
Design a real-time system that scores financial transactions for fraud risk and blocks/flags suspicious activity before it completes.
01 - Why interviewers ask this
It tests a layered real-time-vs-batch architecture — interviewers check if you separate fast, cheap rule checks (sub-50ms) from slower, deeper analysis instead of trying to do everything synchronously.
02 - Where this system exists in the real world
You interact with this design every day.
Stripe / Visa / PayPal fraud-detection pipelines
E-commerce checkout fraud screening
Banking real-time transaction monitoring
03 - What you'll master
Solve this once. Know it forever.
Separate a fast synchronous path from deep analysis
Use precomputed features for low-latency scoring
Design a feedback loop from confirmed fraud outcomes
04 - What you'll design
6 functional · 3 non-functional requirements.
Score an incoming transaction for fraud risk in real time, before it's approved
5 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
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