Referral Tracking Low-Level Design: Attribution, Fraud Detection, and Reward Issuance
A referral tracking system attributes new user signups to the existing user who referred them, enabling reward programs and measuring […]
System Design
System Design
Poll System Low-Level Design: Duplicate Vote Prevention, Real-Time Results, and Multi-Select
A poll system lets users create questions with multiple choice answers, vote on them, and see real-time results. Used in
System Design
Bookmark System Low-Level Design: Folders, Sync, and Full-Text Search
A bookmark (save) system lets users collect and organize content they want to revisit — articles, products, listings, posts. Core
System Design
Content Tagging System Low-Level Design: Normalization, Autocomplete, and Tag-Based Search
A content tagging system lets users and systems attach descriptive labels to content — blog posts, products, images, videos —
System Design
Report and Abuse System Low-Level Design: Triage, Moderator Queue, and Auto-Enforcement
A content reporting and abuse detection system allows users to flag harmful content — spam, harassment, hate speech, illegal material
System Design
Idempotency Key Service Low-Level Design: Deduplication, Atomic Claims, and Concurrent Retries
An idempotency key service ensures that retried API requests do not cause duplicate side effects — a critical requirement for
System Design
Multi-Factor Authentication Low-Level Design: TOTP, SMS OTP, Backup Codes, and Replay Prevention
Multi-factor authentication (MFA) adds a second verification layer beyond passwords — protecting accounts even when passwords are compromised. The three
System Design
Data Archival Low-Level Design: Tiered Storage, Partition Detach, and S3 Cold Storage
A data archival system moves aged, infrequently accessed data from hot storage (fast, expensive) to warm or cold tiers (slower,
System Design
Cache Warming Low-Level Design: Pre-warm Strategies, Stampede Prevention, and Scale-out Warm-up
Cache warming ensures a cache is pre-populated with frequently accessed data before users experience cache misses. Without warming, a fresh
System Design
Trending Topics Low-Level Design: Sliding Window Counts, Time Decay, and Top-K Computation
A trending topics system surfaces content gaining rapid engagement — the top hashtags on Twitter, trending searches on Google, or
System Design
Follower Graph Low-Level Design: Fan-out on Write, Celebrity Problem, and Feed Generation
A follower graph stores directed relationships between users — Alice follows Bob, but Bob may not follow Alice. It powers
System Design
Order Tracking Low-Level Design: State Machine, Carrier Webhooks, and Split Shipments
An order tracking system maintains the lifecycle of a purchase from placement through delivery, providing real-time status to customers and
System Design
Shopping Cart and Checkout Low-Level Design: Price Locking, Inventory Reservation, and Atomic Checkout
A shopping cart and checkout system manages the in-progress purchase state from item addition through payment completion. Core challenges: persisting
System Design
Payment Processing Low-Level Design: Idempotency, Stripe Integration, and Webhook Handling
A payment processing pipeline accepts customer payment details, communicates with a payment processor (Stripe, Braintree, Adyen), and reliably records the
System Design
User Presence System Low-Level Design: Online Status, Heartbeat, and Real-Time Fan-out
A user presence system tracks whether users are online, offline, or idle — powering the green dots in Slack, WhatsApp,