# ScaleMock

> ScaleMock is an SDE interview preparation platform for System Design (HLD),
> Low Level Design (LLD / machine coding), DSA, and frontend rounds, with curated
> problem sheets and AI-powered mock interviews. Last updated: 2026-07-16.

## System Design Sheet (HLD)

The ScaleMock System Design Sheet is a curated, topic-wise list of 150 high-level
design interview problems, available in 25, 75, and 150 problem tiers.

- [System Design Sheet (HLD)](https://scalemock.com/sheet/system-design): curated HLD problems across 25/75/150 tiers.
- [All HLD problems](https://scalemock.com/hld): full high-level design problem bank.

### HLD Problems
- [Design a URL Shortener (TinyURL)](https://scalemock.com/hld/design-url-shortener)
- [Design Instagram (Photo Sharing)](https://scalemock.com/hld/design-instagram)
- [Design a Rate Limiter](https://scalemock.com/hld/design-rate-limiter)
- [Design a Chat System (WhatsApp)](https://scalemock.com/hld/design-chat-system)
- [Design a Notification System](https://scalemock.com/hld/design-notification-system)
- [Design YouTube (Video Streaming)](https://scalemock.com/hld/design-youtube)
- [Design Netflix (Video Streaming)](https://scalemock.com/hld/design-netflix)
- [Design Google Drive (File Storage)](https://scalemock.com/hld/design-google-drive)
- [Design Twitter (Social Graph & Feed)](https://scalemock.com/hld/design-twitter)
- [Design Uber (Ride Hailing)](https://scalemock.com/hld/design-uber)
- [Design a Web Crawler](https://scalemock.com/hld/design-web-crawler)
- [Design Amazon (E-commerce)](https://scalemock.com/hld/design-amazon)
- [Design Ticketmaster (Booking System)](https://scalemock.com/hld/design-ticketmaster)
- [Design Tinder (Location-based Matching)](https://scalemock.com/hld/design-tinder)
- [Design Google Maps (Location Service)](https://scalemock.com/hld/design-google-maps)
- [Design Zoom (Video Conferencing)](https://scalemock.com/hld/design-zoom)
- [Design Spotify (Audio Streaming)](https://scalemock.com/hld/design-spotify)
- [Design Reddit (Discussion Forum)](https://scalemock.com/hld/design-reddit)
- [Design Airbnb (Hotel Booking)](https://scalemock.com/hld/design-airbnb)
- [Design Dropbox (File Sync)](https://scalemock.com/hld/design-dropbox)
- [Design Discord (Voice & Chat)](https://scalemock.com/hld/design-discord)
- [Design Payment Gateway (Stripe)](https://scalemock.com/hld/design-payment-gateway)
- [Design Leaderboard System](https://scalemock.com/hld/design-leaderboard)
- [Design Typeahead Suggestion](https://scalemock.com/hld/design-typeahead)
- [Design Distributed Key-Value Store](https://scalemock.com/hld/design-kv-store)
- [Design News Feed System](https://scalemock.com/hld/design-news-feed)
- [Design Google Docs (Collaborative Editing)](https://scalemock.com/hld/design-google-docs)
- [Design a Distributed Job Scheduler](https://scalemock.com/hld/design-job-scheduler)
- [Design a Metrics Monitoring System](https://scalemock.com/hld/design-metrics-monitoring)
- [Design a Distributed Logging System](https://scalemock.com/hld/design-logging-system)
- [Design a Stock Exchange](https://scalemock.com/hld/design-stock-exchange)
- [Design DoorDash (Food Delivery)](https://scalemock.com/hld/design-doordash)
- [Design Nearby Friends](https://scalemock.com/hld/design-nearby-friends)
- [Design a Distributed Lock Manager](https://scalemock.com/hld/design-distributed-lock)
- [Design an Ad Click Aggregator](https://scalemock.com/hld/design-ad-aggregator)
- [Design an Online Code Judge](https://scalemock.com/hld/design-code-judge)
- [Design a CDN (Content Delivery Network)](https://scalemock.com/hld/design-cdn)
- [Design a Digital Wallet](https://scalemock.com/hld/design-digital-wallet)
- [Design a Fantasy Sports System](https://scalemock.com/hld/design-fantasy-sports)
- [Design an IoT Fleet Management System](https://scalemock.com/hld/design-iot-fleet)
- [Design a Distributed File System](https://scalemock.com/hld/design-dfs)
- [Design a Malware Scanning Service](https://scalemock.com/hld/design-malware-scanner)
- [Design a Flash Sale System](https://scalemock.com/hld/design-flash-sale)
- [Design a Recommendation System](https://scalemock.com/hld/design-recommendation-system)
- [Design a Top-K Frequent Elements Service](https://scalemock.com/hld/design-top-k)
- [Design a Distributed Counter](https://scalemock.com/hld/design-distributed-counter)
- [Design Robinhood (Stock Trading App)](https://scalemock.com/hld/design-robinhood)
- [Design Splitwise (Expense Sharing)](https://scalemock.com/hld/design-splitwise)
- [Design Cricinfo (Live Sports Scoring)](https://scalemock.com/hld/design-cricinfo)
- [Design Pastebin (Text Storage)](https://scalemock.com/hld/design-pastebin)
- [Design Google Calendar (Scheduling)](https://scalemock.com/hld/design-google-calendar)
- [Design Yelp (Local Search)](https://scalemock.com/hld/design-yelp)
- [Design Pinterest (Visual Discovery)](https://scalemock.com/hld/design-pinterest)
- [Design Coursera (Learning Platform)](https://scalemock.com/hld/design-coursera)
- [Design Zepto (Quick Commerce)](https://scalemock.com/hld/design-zepto)
- [Design IRCTC (Railway Booking)](https://scalemock.com/hld/design-irctc)
- [Design UrbanCompany (Home Services)](https://scalemock.com/hld/design-urban-company)
- [Design LinkedIn (Professional Network)](https://scalemock.com/hld/design-linkedin)
- [Design Gmail (Email Service)](https://scalemock.com/hld/design-gmail)
- [Design Google Photos (Cloud Photo Storage)](https://scalemock.com/hld/design-google-photos)
- [Design Truecaller (Caller Identification)](https://scalemock.com/hld/design-truecaller)
- [Design Wikipedia (Knowledge Base)](https://scalemock.com/hld/design-wikipedia)
- [Design GitHub (Version Control Hosting)](https://scalemock.com/hld/design-github)
- [Design StackOverflow (Q&A Platform)](https://scalemock.com/hld/design-stackoverflow)
- [Design CodeSandbox (Online IDE)](https://scalemock.com/hld/design-codesandbox)
- [Design Canva (Online Graphic Design)](https://scalemock.com/hld/design-canva)
- [Design a Unique ID Generator (Snowflake)](https://scalemock.com/hld/design-unique-id-generator)
- [Design a Web Search Engine (Google Search)](https://scalemock.com/hld/design-web-search-engine)
- [Design a Distributed Cache (Redis)](https://scalemock.com/hld/design-distributed-cache)
- [Design a Message Queue (Kafka)](https://scalemock.com/hld/design-message-queue)
- [Design a Live Streaming Platform (Twitch)](https://scalemock.com/hld/design-live-streaming)
- [Design a Collaborative Whiteboard (Miro)](https://scalemock.com/hld/design-collaborative-whiteboard)
- [Design a Feature Flag Management System](https://scalemock.com/hld/design-feature-flag)
- [Design a Distributed Tracing System (Jaeger)](https://scalemock.com/hld/design-distributed-tracing)
- [Design a Crash Reporting System (Sentry)](https://scalemock.com/hld/design-crash-reporting)
- [Design a CI/CD Pipeline Service](https://scalemock.com/hld/design-cicd-pipeline)
- [Design a Digital Signature Service (DocuSign)](https://scalemock.com/hld/design-digital-signature)
- [Design a Virtual Waiting Room](https://scalemock.com/hld/design-virtual-waiting-room)
- [Design a Real-time Ad Bidding System](https://scalemock.com/hld/design-ad-bidding)
- [Design a Price Comparison Engine](https://scalemock.com/hld/design-price-comparison)
- [Design a Translation Service (Google Translate)](https://scalemock.com/hld/design-translation-service)
- [Design a MapReduce Framework](https://scalemock.com/hld/design-mapreduce)
- [Design a Location History Service](https://scalemock.com/hld/design-location-history)
- [Design a Podcast Hosting Platform](https://scalemock.com/hld/design-podcast-platform)
- [Design a Newsletter Platform (Substack)](https://scalemock.com/hld/design-newsletter-platform)
- [Design a Survey System (SurveyMonkey)](https://scalemock.com/hld/design-survey-system)
- [Design a Platform as a Service (Heroku)](https://scalemock.com/hld/design-paas)
- [Design a Serverless Compute Platform (AWS Lambda)](https://scalemock.com/hld/design-serverless-platform)
- [Design an Object Storage Service (Amazon S3)](https://scalemock.com/hld/design-object-storage)
- [Design a Domain Name System (DNS)](https://scalemock.com/hld/design-dns)
- [Design a Virtual Private Network (VPN)](https://scalemock.com/hld/design-vpn)
- [Design a Peer-to-Peer File Sharing System (BitTorrent)](https://scalemock.com/hld/design-p2p-file-sharing)
- [Design a Blockchain Ledger (Bitcoin)](https://scalemock.com/hld/design-blockchain)
- [Design a NFT Marketplace (OpenSea)](https://scalemock.com/hld/design-nft-marketplace)
- [Design a Password Manager (LastPass)](https://scalemock.com/hld/design-password-manager)
- [Design a Two-Factor Authentication System (Authy)](https://scalemock.com/hld/design-2fa)
- [Design an Identity Provider (Auth0)](https://scalemock.com/hld/design-identity-provider)
- [Design a Web Application Firewall (WAF)](https://scalemock.com/hld/design-waf)
- [Design a DDoS Protection System](https://scalemock.com/hld/design-ddos-protection)
- [Design a CAPTCHA System (reCAPTCHA)](https://scalemock.com/hld/design-captcha)
- [Design a Plagiarism Checker (Turnitin)](https://scalemock.com/hld/design-plagiarism-checker)
- [Design a Crowdfunding Platform (Kickstarter)](https://scalemock.com/hld/design-crowdfunding)
- [Design a Blogging Platform (Medium)](https://scalemock.com/hld/design-blogging-platform)
- [Design a Telemedicine Platform (Practo)](https://scalemock.com/hld/design-telemedicine)
- [Design a Bike Sharing System (Lime)](https://scalemock.com/hld/design-bike-sharing)
- [Design a Smart Home Automation System](https://scalemock.com/hld/design-smart-home)
- [Design a Supply Chain Management System](https://scalemock.com/hld/design-supply-chain)
- [Design a Traffic Control System](https://scalemock.com/hld/design-traffic-control)
- [Design a Weather Forecasting System](https://scalemock.com/hld/design-weather-system)
- [Design a Digital Library System](https://scalemock.com/hld/design-digital-library)
- [Design a Video Transcoding Service (Handbrake Cloud)](https://scalemock.com/hld/design-video-transcoding)
- [Design a Distributed Database (CockroachDB)](https://scalemock.com/hld/design-distributed-database)
- [Design a Time-Series Database (InfluxDB)](https://scalemock.com/hld/design-time-series-db)
- [Design a Vector Database (Pinecone)](https://scalemock.com/hld/design-vector-db)
- [Design a Graph Database (Neo4j)](https://scalemock.com/hld/design-graph-db)
- [Design a Service Mesh (Istio)](https://scalemock.com/hld/design-service-mesh)
- [Design a Distributed Configuration System (Etcd)](https://scalemock.com/hld/design-distributed-config)
- [Design a Secrets Management System (Vault)](https://scalemock.com/hld/design-secrets-management)
- [Design a Build System (Bazel)](https://scalemock.com/hld/design-build-system)
- [Design an LSM Tree Storage Engine](https://scalemock.com/hld/design-lsm-tree)
- [Design a B-Tree Storage Engine](https://scalemock.com/hld/design-btree-engine)
- [Design a Distributed Transaction Manager](https://scalemock.com/hld/design-transaction-manager)
- [Design a Change Data Capture (CDC) System](https://scalemock.com/hld/design-cdc-system)
- [Design a Data Lakehouse (Delta Lake)](https://scalemock.com/hld/design-data-lakehouse)
- [Design a Real-time Fraud Detection System](https://scalemock.com/hld/design-fraud-detection)
- [Design a Privacy-Preserving Analytics System](https://scalemock.com/hld/design-privacy-analytics)
- [Design a Workflow Orchestration Engine (Airflow)](https://scalemock.com/hld/design-workflow-engine)
- [Design a Real-time Collaborative Spreadsheet](https://scalemock.com/hld/design-collaborative-spreadsheet)
- [Design a Browser Engine (Chrome)](https://scalemock.com/hld/design-browser-engine)
- [Design a JavaScript Runtime (Node.js)](https://scalemock.com/hld/design-js-runtime)
- [Design a Virtual Machine (JVM)](https://scalemock.com/hld/design-virtual-machine)
- [Design a Load Balancer (NGINX)](https://scalemock.com/hld/design-load-balancer)
- [Design a VPN Protocol (WireGuard)](https://scalemock.com/hld/design-vpn-protocol)
- [Design an Onion Routing Network (Tor)](https://scalemock.com/hld/design-onion-routing)
- [Design a DFS Metadata Service (NameNode)](https://scalemock.com/hld/design-namenode)
- [Design a Garbage Collector](https://scalemock.com/hld/design-garbage-collector)
- [Design a To-Do List App](https://scalemock.com/hld/design-todo-app)
- [Design a Parking Lot System](https://scalemock.com/hld/design-parking-lot)
- [Design an Image Hosting Service (Imgur)](https://scalemock.com/hld/design-image-hosting)
- [Design a QR Code Generator](https://scalemock.com/hld/design-qr-code-generator)
- [Design a Poll/Voting System](https://scalemock.com/hld/design-poll-system)
- [Design a ChatGPT-style LLM Serving System](https://scalemock.com/hld/design-llm-serving)
- [Design a RAG (Retrieval-Augmented Generation) Pipeline](https://scalemock.com/hld/design-rag-pipeline)
- [Design a Feature Store (Feast/Tecton-style)](https://scalemock.com/hld/design-feature-store)
- [Design a Batch Inference API for a GPU Cluster](https://scalemock.com/hld/design-batch-inference)
- [Design an ML Experiment Tracking & Model Registry (MLflow-style)](https://scalemock.com/hld/design-model-registry)
- [Design an LLM Fine-tuning / RLHF Training Pipeline](https://scalemock.com/hld/design-llm-finetuning)
- [Design a Health Monitoring & On-call Alerting System (PagerDuty-style)](https://scalemock.com/hld/design-alerting-system)
- [Design a Container Orchestration Platform (Kubernetes-style)](https://scalemock.com/hld/design-container-orchestration)
- [Design a Cloud Cost Attribution & FinOps Platform](https://scalemock.com/hld/design-finops-platform)

## Low Level Design Sheet (LLD)

The ScaleMock Low Level Design Sheet is a curated, topic-wise list of 150 machine-coding
and object-oriented design problems, available in 25, 75, and 150 problem tiers.

- [Low Level Design Sheet (LLD)](https://scalemock.com/sheet/low-level-design): curated LLD problems across 25/75/150 tiers.
- [All LLD problems](https://scalemock.com/lld): full low-level design problem bank.

### LLD Problems
- [Design a Parking Lot](https://scalemock.com/lld/parking-lot)
- [Design an Elevator System](https://scalemock.com/lld/elevator-system)
- [Design a Library Management System](https://scalemock.com/lld/library-management)
- [Design Snake and Ladder Game](https://scalemock.com/lld/snake-ladder)
- [Design Splitwise (Expense Sharing)](https://scalemock.com/lld/splitwise)
- [Design a Hotel Booking System](https://scalemock.com/lld/hotel-booking)
- [Design Movie Ticket Booking](https://scalemock.com/lld/movie-ticket-booking)
- [Design a Chess Game](https://scalemock.com/lld/chess-game)
- [Design a Vending Machine](https://scalemock.com/lld/vending-machine)
- [Design a Stock Brokerage System](https://scalemock.com/lld/stock-broker)
- [Design an E-Commerce Platform](https://scalemock.com/lld/online-shopping)
- [Design a Car Rental System](https://scalemock.com/lld/car-rental)
- [Design Tic-Tac-Toe](https://scalemock.com/lld/tic-tac-toe)
- [Design a URL Shortener](https://scalemock.com/lld/url-shortener)
- [Design a Chat Application](https://scalemock.com/lld/chat-application)
- [Design an ATM](https://scalemock.com/lld/atm-machine)
- [Design Cricinfo/Cricbuzz](https://scalemock.com/lld/cricinfo)
- [Design In-Memory File System](https://scalemock.com/lld/file-system)
- [Design a Task Scheduler](https://scalemock.com/lld/task-scheduler)
- [Design a Logging Framework](https://scalemock.com/lld/logger-system)
- [Design a Rate Limiter](https://scalemock.com/lld/rate-limiter)
- [Design LRU Cache](https://scalemock.com/lld/lru-cache)
- [Design Swiggy/Zomato](https://scalemock.com/lld/food-delivery)
- [Design Uber/Ola](https://scalemock.com/lld/cab-booking)
- [Design Notification Service](https://scalemock.com/lld/notification-service)
- [Design Twitter/Instagram Feed](https://scalemock.com/lld/social-media-feed)
- [Design Unix Find Command](https://scalemock.com/lld/find-command)
- [Design Spotify Music Player](https://scalemock.com/lld/music-player)
- [Design Airbnb Review System](https://scalemock.com/lld/airbnb-review)
- [Design Digital Wallet System](https://scalemock.com/lld/wallet-system)
- [Design Pizza Ordering System](https://scalemock.com/lld/pizza-pricing)
- [Design LinkedIn Connections](https://scalemock.com/lld/linkedin-connection)
- [Design Meeting Room Scheduler](https://scalemock.com/lld/conference-scheduler)
- [Design HashMap from Scratch](https://scalemock.com/lld/hash-map)
- [Design Online Auction System](https://scalemock.com/lld/online-auction)
- [Design Text Editor with Undo/Redo](https://scalemock.com/lld/text-editor)
- [Design Traffic Light System](https://scalemock.com/lld/traffic-light)
- [Design Stack Overflow](https://scalemock.com/lld/stack-overflow)
- [Design Excel/Google Sheets](https://scalemock.com/lld/spreadsheet)
- [Design Google Calendar](https://scalemock.com/lld/calendar-app)
- [Design Blackjack Card Game](https://scalemock.com/lld/blackjack)
- [Design Instagram Photo Sharing](https://scalemock.com/lld/photo-sharing)
- [Design Food Court Order System](https://scalemock.com/lld/food-court)
- [Design Cricket Scoreboard](https://scalemock.com/lld/cricket-scoreboard)
- [Design Coupon/Discount System](https://scalemock.com/lld/coupon-system)
- [Design Minesweeper Game](https://scalemock.com/lld/minesweeper)
- [Design a Coffee Machine](https://scalemock.com/lld/coffee-machine)
- [Design a Quiz System](https://scalemock.com/lld/quiz-system)
- [Design Airline Management System](https://scalemock.com/lld/airline-management)
- [Design Warehouse Management](https://scalemock.com/lld/warehouse-management)
- [Design Smart Home System](https://scalemock.com/lld/smart-home)
- [Design Train Platform System](https://scalemock.com/lld/train-platform)
- [Design Surge Pricing System](https://scalemock.com/lld/surge-pricing)
- [Design Plagiarism Checker](https://scalemock.com/lld/plagiarism-checker)
- [Design Version Control (Git)](https://scalemock.com/lld/version-control)
- [Design Amazon Locker](https://scalemock.com/lld/locker-system)
- [Design Payment Gateway](https://scalemock.com/lld/payment-gateway)
- [Design Online Coding Judge](https://scalemock.com/lld/coding-judge)
- [Design Fantasy Sports (Dream11)](https://scalemock.com/lld/fantasy-sports)
- [Design Distributed Message Queue](https://scalemock.com/lld/message-queue)
- [Design Real-Time Leaderboard](https://scalemock.com/lld/leaderboard-system)
- [Design Distributed Key-Value Store](https://scalemock.com/lld/key-value-store)
- [Design Content Delivery Network (CDN)](https://scalemock.com/lld/cdn-system)
- [Design Metrics Monitoring System](https://scalemock.com/lld/metrics-monitoring)
- [Design Collaborative Whiteboard](https://scalemock.com/lld/collaborative-whiteboard)
- [Design Subscription System](https://scalemock.com/lld/subscription-system)
- [Design Search Autocomplete](https://scalemock.com/lld/search-autocomplete)
- [Design Web Crawler](https://scalemock.com/lld/web-crawler)
- [Design Google Maps Navigation](https://scalemock.com/lld/map-navigation)
- [Design Ad Click Analytics](https://scalemock.com/lld/ad-analytics)
- [Design Flash Sale System](https://scalemock.com/lld/flash-sale)
- [Design Zoom (Video Conference)](https://scalemock.com/lld/video-conferencing)
- [Design Dating App (Tinder)](https://scalemock.com/lld/dating-app)
- [Design Investment Platform (Robinhood)](https://scalemock.com/lld/investment-platform)
- [Design Digital Newsstand (Medium)](https://scalemock.com/lld/digital-newsstand)
- [Design CI/CD Pipeline (Jenkins)](https://scalemock.com/lld/cicd-pipeline)
- [Design Real-time Bidding (eBay)](https://scalemock.com/lld/bidding-system)
- [Design E-Voting System](https://scalemock.com/lld/voting-system)
- [Design Database Connection Pool](https://scalemock.com/lld/connection-pool)
- [Design Business Rule Engine](https://scalemock.com/lld/rule-engine)
- [Design Feature Flag Service](https://scalemock.com/lld/feature-flag)
- [Design JSON Parser](https://scalemock.com/lld/json-parser)
- [Design IAM (Role Based Access Control)](https://scalemock.com/lld/iam-system)
- [Design Circuit Breaker Pattern](https://scalemock.com/lld/circuit-breaker)
- [Design Distributed Lock Manager](https://scalemock.com/lld/distributed-lock)
- [Design Log Forwarder (Fluentd)](https://scalemock.com/lld/log-forwarder)
- [Design Distributed Job Scheduler (Cron)](https://scalemock.com/lld/job-scheduler)
- [Design In-Memory File System](https://scalemock.com/lld/in-memory-fs)
- [Design Build System (Bazel/Make)](https://scalemock.com/lld/build-system)
- [Design Load Balancer (L7)](https://scalemock.com/lld/load-balancer)
- [Design Distributed ID Generator (Snowflake)](https://scalemock.com/lld/distributed-id-generator)
- [Design Webhook Delivery Service](https://scalemock.com/lld/webhook-service)
- [Design P2P File Sharing (BitTorrent)](https://scalemock.com/lld/p2p-bittorrent)
- [Design Payment Reconciliation](https://scalemock.com/lld/payment-reconciliation)
- [Design Loyalty & Rewards System](https://scalemock.com/lld/loyalty-system)
- [Design Fraud Detection System](https://scalemock.com/lld/fraud-detection)
- [Design Distributed Tracing (Jaeger)](https://scalemock.com/lld/distributed-tracing)
- [Design Container Scheduler (K8s)](https://scalemock.com/lld/container-scheduler)
- [Design Google Docs (Real-time)](https://scalemock.com/lld/collaborative-editor)
- [Design Deployment System](https://scalemock.com/lld/deployment-system)
- [Design Stock Matching Engine](https://scalemock.com/lld/matching-engine)
- [Design Recommendation Engine](https://scalemock.com/lld/recommendation-engine)
- [Design Distributed Database (Spanner)](https://scalemock.com/lld/distributed-database)
- [Design OS Kernel Scheduler](https://scalemock.com/lld/os-scheduler)
- [Design Garbage Collector (V8)](https://scalemock.com/lld/garbage-collector)
- [Design Distributed File System (HDFS)](https://scalemock.com/lld/distributed-file-system)
- [Design Browser Layout Engine](https://scalemock.com/lld/browser-engine)
- [Design Distributed Video Transcoder](https://scalemock.com/lld/video-transcoder)
- [Design a Thread-safe Singleton Logger](https://scalemock.com/lld/singleton-logger)
- [Design a Fluent Query Builder](https://scalemock.com/lld/query-builder)
- [Design a Cross-Platform UI Widget Factory](https://scalemock.com/lld/ui-widget-factory)
- [Design a Vehicle Factory (Factory Method)](https://scalemock.com/lld/vehicle-factory)
- [Design an Object Prototype Registry](https://scalemock.com/lld/prototype-registry)
- [Design a Maze / Game Map Generator](https://scalemock.com/lld/maze-game-builder)
- [Design a Payment Gateway Adapter](https://scalemock.com/lld/payment-adapter)
- [Design a Beverage Add-on System (Decorator)](https://scalemock.com/lld/beverage-decorator)
- [Design a Lazy-Loading Video Proxy](https://scalemock.com/lld/video-proxy)
- [Design an Emoji/Icon Flyweight Renderer](https://scalemock.com/lld/emoji-flyweight)
- [Design a Multi-Database Bridge](https://scalemock.com/lld/db-bridge)
- [Design a Stock Price Observer System](https://scalemock.com/lld/stock-observer)
- [Design an Order Processing Pipeline (Chain of Responsibility)](https://scalemock.com/lld/order-chain)
- [Design a Trip Fare Calculator (Strategy)](https://scalemock.com/lld/fare-strategy)
- [Design a File System Iterator (DFS/BFS)](https://scalemock.com/lld/fs-iterator)
- [Design a Form Validation Template Method](https://scalemock.com/lld/form-template-method)
- [Design an Interpreter for a Simple DSL](https://scalemock.com/lld/dsl-interpreter)
- [Refactor a God-Class Payroll System (SRP)](https://scalemock.com/lld/payroll-srp)
- [Design an Extensible Shape Area Calculator (OCP)](https://scalemock.com/lld/shape-area-ocp)
- [Design a Bird Hierarchy (LSP — Penguin Problem)](https://scalemock.com/lld/bird-lsp)
- [Design a Printer Interface Segregation (ISP)](https://scalemock.com/lld/printer-isp)
- [Design a Notification Service with DI (DIP)](https://scalemock.com/lld/notification-dip)
- [Design a Pluggable Payment Provider (All SOLID)](https://scalemock.com/lld/pluggable-payment-solid)
- [Design an Immutable Value Object (Money)](https://scalemock.com/lld/immutable-money)
- [Design a Bounded Blocking Queue](https://scalemock.com/lld/bounded-blocking-queue)
- [Design a Thread Pool Executor](https://scalemock.com/lld/thread-pool)
- [Design a Read-Write Lock](https://scalemock.com/lld/read-write-lock)
- [Design a Solution to Dining Philosophers](https://scalemock.com/lld/dining-philosophers)
- [Design a Producer-Consumer System](https://scalemock.com/lld/producer-consumer)
- [Design a Thread-safe In-Memory Registry](https://scalemock.com/lld/thread-safe-registry)
- [Design a Fluent HTTP Client SDK](https://scalemock.com/lld/http-client-sdk)
- [Design a Pagination & Cursor API](https://scalemock.com/lld/pagination-api)
- [Design a Retry with Backoff Policy](https://scalemock.com/lld/retry-backoff)
- [Design an In-Process Event Bus](https://scalemock.com/lld/event-bus)
- [Design an Object Mapper / Serializer](https://scalemock.com/lld/object-mapper)
- [Design Conway's Game of Life](https://scalemock.com/lld/game-of-life)
- [Design a Sudoku Validator & Solver](https://scalemock.com/lld/sudoku-validator)
- [Design the Connect Four Game](https://scalemock.com/lld/connect-four)
- [Design an Inventory Management System](https://scalemock.com/lld/inventory-management)
- [Design an LFU Cache](https://scalemock.com/lld/lfu-cache)
- [Design an In-Memory Database with Transactions](https://scalemock.com/lld/in-memory-db-txn)
- [Design a Meeting Room Scheduler](https://scalemock.com/lld/meeting-scheduler)

## Practice & Learn

- [DSA problems](https://scalemock.com/dsa): company-specific data structures and algorithms.
- [Frontend / online assessments](https://scalemock.com/frontend): machine-coding and OA practice.
- [AI mock interviews](https://scalemock.com/mock-interview): AI-driven DSA, HLD, and LLD mocks.
- [System Design course](https://scalemock.com/learn/hld): HLD concept lessons.
- [Low Level Design course](https://scalemock.com/learn/lld): LLD concept lessons.