Designing a Delivery Route Optimization System for a Multi-Order Courier Fleet How platforms with hundreds of couriers — each juggling several simultaneous orders — decide who picks up what, in what order, and along which route, balancing delivery speed, fairness, and fleet-wide efficiency at scale. A full architectural walkthrough from…

Designing a Collaborative Code Editor — System Design A complete, ground-up walkthrough of how real-time, multi-user code editors like Google Docs for code, VS Code Live Share, Replit and CodeSandbox are actually built — from the first keystroke to global, low-latency, always-consistent editing at scale. 01 · The Big Idea02…

Designing a Low-Latency Live-Streaming System for Interactive Use Cases How do you get a bid, a raised hand, or an auctioneer’s hammer to appear on thousands of viewers’ screens in well under a second? A deep, interview-grade walkthrough of building a glass-to-glass sub-second live streaming pipeline for real-time interactive experiences…

Real-Time FX Arbitrage Detection System Design Designing a low-latency, safety-critical system for a multi-currency trading desk to detect and capture profitable rate discrepancies across venues before they disappear — ingestion, triangular and cross-venue detection, risk, execution, and everything the desk needs to actually trust it. 01 · Intro & History…

Designing a Real-Time Net Worth & Portfolio Valuation System A complete system design walkthrough: aggregating holdings across stocks, crypto, real estate, cash, and liabilities into one live, always-accurate number — at millions of requests per minute. 01 · Introduction02 · Problem03 · Architecture04 · Internal Working05 · Data Flow06 ·…

Designing a Real-Time Cross-Border Remittance Platform with Transparent Fee Calculation A production-grade walkthrough for engineers and architects: how to move money across borders in seconds, quote fees the sender can trust before they tap confirm, and keep the whole thing correct even when a bank on the other side of…

Designing Real-Time Language Translation for Live Video Calls A complete system design walkthrough covering architecture, ASR / MT / TTS pipelines, WebRTC media routing, latency budgeting, scaling to millions of concurrent minutes, reliability, and security — written for interview preparation and real production understanding. 01 · Introduction02 · The Problem03…

Automated Portfolio Rebalancing Engine for Robo-Advisors A deep, production-grade system design walkthrough — architecture, data flow, scaling to millions of accounts, tax-aware trading, order netting, and interview-ready trade-off discussions. Threshold-driven rebalancing at retail scale, without the transaction costs eating the alpha. 01 · Intro & History 02 · Architecture 03…

Designing a Real-Time Settlement Risk Management System How payments platforms decide, transaction by transaction, exactly how much settlement credit a merchant can safely be given — without ever letting risk exposure cross the line. 01 · Introduction02 · Foundations03 · Architecture04 · Internal Working05 · Data Flow06 · Concurrency07 ·…

Designing Strong Customer Authentication for a European Payments Platform A complete, interview-ready system design guide for engineers building risk-based authentication systems that satisfy PSD2’s mandated two-factor requirements while keeping low-risk checkout as frictionless as possible. 01 · Introduction02 · Regulatory03 · Architecture04 · Internal Working05 · Data Flow06 · Trade-offs07…