Designing an Automated Tax Document Generation System (1099 Forms) for a Gig Payments Platform A production-grade system design walkthrough for engineers building compliant, scalable tax reporting infrastructure that must serve millions of independent contractors correctly, within a narrow, immovable January filing window. 01 · Intro & History02 · Problem03 ·…

Designing a Card Tokenization System for Payments A complete, production-grade system design walkthrough for replacing sensitive card numbers with non-sensitive tokens across an entire payment processing pipeline, at the scale of a major card processor — covering architecture, algorithms, security, scalability, availability, deployment and real-world industry patterns. 01 · Intro…

Designing an Authorized Push Payment Scam Detection System A complete, beginner-to-production system design walkthrough: how to detect, in real time, when a genuine customer is being manipulated into authorizing their own fraudulent transfer — and how to intervene before the money is irreversibly gone — using behavioural profiling, graph-based payee…

Real-Time Aggregate Credit Line Utilization Tracking Across Multiple Credit Products A production-grade system design guide for engineers and architects building shared-limit credit enforcement systems at bank scale — covering architecture, concurrency, consistency, resilience, and the patterns that real financial institutions actually use. 01 · Intro & History02 · Architecture03 ·…

Currency Conversion Engine for International Remittance How to design a system that shows a customer an exchange rate and then guarantees, at massive scale, that the money actually moves at that exact rate — covering architecture, rate locking, consistency, and a million-requests-per-minute scaling plan. 01 · Introduction02 · Problem03 ·…

Designing a Real-Time Shipment Tracking System at Scale A complete, from-first-principles walkthrough of how large e-commerce and logistics platforms aggregate shipment status from many third-party carriers — FedEx, UPS, DHL, USPS, and regional couriers — and present customers with one unified, near-real-time tracking timeline. 01 · Intro & History02 ·…

System Design · Trust, Aggregation & Fake Review Detection Designing a Scalable Product Reviews & Ratings System How marketplaces at the scale of hundreds of millions of products and billions of reviews collect star ratings and written feedback, aggregate them in real time, and — critically — detect and stop…

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Designing a Real-Time Seller Analytics Dashboard A complete, from-first-principles walkthrough of how large marketplaces build systems that give millions of independent sellers a live view of their own sales, traffic, and conversion metrics — updated in near real time, accurate down to the last order, and fast enough to feel…

Designing a Returns & Refunds Processing System at Scale A complete, ground-up engineering guide to building a system that processes millions of returns and refunds a month accurately, quickly, and without losing a single dollar to reconciliation errors. 01 · Intro & History02 · Problem03 · Core Concepts04 · Architecture05…