Low-level design practice
Low-Level Design and Object-Oriented Design Interview Questions
Practice turning requirements into clear objects, interfaces, interactions, and extensible implementations with guided low-level design exercises.
Recently updated practice
Start with a guided exercise
These recently observed catalog entries show the full guided format. Company tags and dates reflect the public catalog; they do not guarantee a company's current interview process.
Design a Return Drop-Store Booking System
Model how a customer finds an eligible nearby drop store, reserves a slot, and hands over a return package.
AmazonCatalog signal Sep 202680 min5 checkpointsJunior, Mid-level, SeniorDesign a Thread-Safe Queryable Logger Library
Model concurrent structured-log appends and filtered retrieval with stable ordering and snapshot semantics.
SentinelOneCatalog signal Sep 202665 min5 checkpointsJunior, Mid-level, SeniorDesign and Implement a Concurrent Web Crawler Library
Coordinate bounded parallel fetching, exact URL admission, cancellation, and race-safe session completion in one process.
SentinelOneCatalog signal Sep 202670 min5 checkpointsSeniorDesign and Implement a Train Route Fare Calculator
Model an ordered train route, sum its per-segment fares, and apply a deterministic weekend cap.
AmazonCatalog signal Sep 202648 min5 checkpointsJuniorDesign a Bookshelf with Reading Progress
Design a personal bookshelf whose CRUD operations preserve a valid, durable bookmark for every existing book.
GoogleCatalog signal Sep 202645 min4 checkpointsMid-levelDesign a Multi-Channel Bot Notification Service
Model notification fanout across email, SMS, and Slack when each channel can have multiple bot integrations.
OpenAICatalog signal Aug 202655 min4 checkpointsJunior, Mid-level, SeniorDesign an In-Memory File System
Model an in-memory hierarchical file system with explicit path, entry, listing, and concurrency contracts.
Uber FreightCatalog signal Aug 202645 min4 checkpointsMid-levelDesign a Movie Ticket Booking System
Model a customer journey that holds seats for a scheduled show and safely turns a valid hold into a booking.
ClearTaxCatalog signal Aug 202660 min5 checkpointsJunior, Mid-level, SeniorDesign and Implement Ride Dispatch and Trip Lifecycle
Model the objects and executable core for requesting a ride, assigning one available driver, and completing or cancelling the trip safely.
UberCatalog signal Aug 202674 min5 checkpointsMid-levelDesign an Extensible Multi-Channel Alerting Platform
Model an alerting core that can add alert categories and delivery channels without rewriting its dispatcher.
AmazonOmnissaCatalog signal Aug 202655 min4 checkpointsMid-levelDesign and Implement an Active-Passive Key-Value Store
Model and implement an in-memory key-value store whose writes commit to active and passive replicas together or fail without changing either.
OracleCatalog signal Aug 202650 min5 checkpointsJunior, Mid-level, SeniorDesign an Elevator Control System
Model elevator cars, hall and cabin requests, dispatch assignment, movement state, and safe fault handling.
SalesforceCatalog signal Aug 202645 min4 checkpointsMid-level, Senior
Complete public index
Browse every exercise by primary topic
All 60 titles below link directly to a guided exercise. The compact index keeps the complete library discoverable without turning this page into an oversized copy of every problem briefing.
Concurrency
23- Design a Return Drop-Store Booking System
- Design a Thread-Safe Queryable Logger Library
- Design and Implement a Concurrent Web Crawler Library
- Design an In-Memory File System
- Design a Movie Ticket Booking System
- Design and Implement Ride Dispatch and Trip Lifecycle
- Design and Implement an Active-Passive Key-Value Store
- Design an In-Memory Job Scheduler
- Design an In-Memory Action Rate Limiter
- Design an In-Memory Read-Through Cache
- Design a Multi-Stage Audio Buffer Pipeline
- Design a Library Circulation System
- Design a Promotion Display Decision Engine
- Design a Locking Key-Value Store with Batch Writes
- Design a WAL-Backed Batch Log Writer
- Design and Implement a Parking Lot
- Design Music Search, Playlists, and Playback
- Design and Implement an In-Memory Tally Service
- Design and Implement a Pluggable Notification Rate Limiter
- Design and Repair a Thread-Safe Configuration Singleton
- Design a Brokerage Order Processing Domain
- Design Tagged Gift Shop Search
- Air Traffic Control System
Object Modeling
23- Design an Elevator Control System
- Design a Connect Four Game
- Design a Job Marketplace Domain
- Design a Workflow Orchestrator Domain
- Design a Parking Lot with Flexible Fees
- Desktop Notification Center
- Design a Cash Register with Inventory and Profit Tracking
- Design a Database Partition Split-and-Merge Manager
- Refactor a Cache for Pluggable Eviction Policies
- Design File-System Search with Symlink Safety
- Design a Configurable Logging Framework
- Design and Implement a Doubly Linked List
- Design and Implement an ATM Machine
- Design a Payments and Cards Domain
- Design and Implement an In-Memory Relational Database Engine
- Warehouse Order Transit Tracking
- Design a Threaded Comment System with User Tags
- Design an Annotated Comment Thread System
- Design a Dating Application
- Design a Location-Aware Dating Application
- Design a Recurring Grocery Subscription Domain
- Design Undo Delete for Shared Collections
- Design Undoable Deletion for API Collections
Extensibility
8- Design a Multi-Channel Bot Notification Service
- Design an Extensible Multi-Channel Alerting Platform
- Design an Extensible Text Editor
- Design a Blackjack Table Game
- Design Infinite Scroll for Mutable Data
- Design a Multi-Floor Parking Lot
- Design a Rectangular Jigsaw Puzzle
- Design and Implement a Battleship Game
Design Patterns
4Interfaces
2Questions about the library
How to use this practice collection
- What is covered in the low-level design library?
- The current public library contains 60 guided exercises spanning object modeling, interfaces, design patterns, extensibility, state management, concurrency, and testing.
- Is low-level design the same as object-oriented design?
- They overlap heavily in software engineering interviews. These exercises emphasize clear object responsibilities, interfaces, interactions, extension points, and implementation tradeoffs rather than large distributed-system architecture.
- How should I practice an LLD interview question?
- Start with requirements and constraints, identify the core objects, define interfaces and interactions, then explain how the model changes under a new requirement. Use code only after the design boundaries are clear.