It’s not just about “designing a system” — it’s also about how you can augment traditional designs with AI smartness when required.
Low-Level Design (LLD) has become the bread and butter of interviews, regardless of experience, language, or company level. Whether it’s a startup or a FAANG company, everyone wants to see how well you can think in terms of modularity, scalability, and real-world abstractions. And in today’s GenAI-infused world, it’s not just about “designing a system” — it’s also about how you can augment traditional designs with AI smartness when required.
Let’s start with a master list of the most frequently asked and high-impact LLD questions across companies like Amazon, Google, Microsoft, Flipkart, Uber, and now OpenAI or any AI-driven company.
1. Design a Parking Lot
- Model different types of parking spots (compact, large, handicapped, etc.)
- Handle multiple vehicle types (car, bike, truck) with varying space requirements
- Design entry and exit flow, including ticket generation and payment
- Consider concurrency — multiple cars entering and exiting simultaneously
- Extend for multi-level or multi-zone parking structures
2. Design a Library Management System
- Define entities like Book, User (Librarian, Member), Catalog, and LibraryCard
- Include operations such as search, checkout, return, renew, and reserve
- Handle fines for late return and book hold queue
- Add features like digital catalog browsing, notifications for due dates
- Think about scalability: thousands of users and books in a large system
3. Design an Elevator System
- Model elevator state (idle, moving up, down, loading)
- Support multiple elevators with coordination logic (e.g., nearest elevator selection)
- Handle user requests from floors and within elevators
- Introduce prioritization (VIP, emergency mode, peak hours)
- Discuss concurrency and scheduling of movements
4. Design a Snake and Ladder Game
- Represent the board, players, snakes, ladders, and dice
- Maintain game state turn-by-turn
- Handle multiple players in a fair rotation
- Make the design extensible for custom boards or other board games
- Consider UI integration and separation of game logic from rendering
5. Design Splitwise
- Handle user groups, expense creation, and balance calculation
- Support various split types (equal, exact amount, percentage)
- Keep track of who owes whom and compute simplified debt graphs
- Extend to include settlement and payment tracking
- Consider scalability if extended to a fintech app
6. Design a Rate Limiter
- Explain and implement token bucket, leaky bucket, or sliding window algorithm
- Apply user-based or API key-based throttling
- Discuss where this would be deployed (API gateway, microservice layer)
- Show how rate limits reset over time
- Handle distributed environments (using Redis, for example)
7. Design a Notification System
- Design producers and consumers for email, SMS, and push notifications
- Use queuing mechanism to support async and retries
- Model templates, prioritization, and scheduling
- Include delivery reports and error tracking
- Discuss how to throttle notifications per user
8. Design an ATM Machine
- Define components like CardReader, Keypad, CashDispenser, Screen
- Model transactions: withdrawal, deposit, transfer, balance inquiry
- Include authentication using PIN and user session management
- Handle money denomination logic (e.g., prefer large notes first)
- Ensure fail-safe handling for partial failures (e.g., cash not dispensed but account debited)
9. Design a Vending Machine
- Model product selection, payment, inventory, and dispensing mechanisms
- Implement state machine for selection, payment, dispensing, and idle
- Support refunds and restocking
- Add concurrency safety when multiple users interact simultaneously
- Extend to accept multiple payment types
10. Design a Movie Ticket Booking System
- Model theaters, screens, seats, shows, and time slots
- Support seat locking and booking with concurrency handling
- Enable search by location, movie, or time
- Handle promotions, cancellations, and refunds
- Prevent race conditions and overbooking using locking mechanisms
11. Design a Ride Sharing App
- Model real-time location tracking for users and drivers
- Include request matching logic between rider and nearby drivers
- Handle pricing (base fare, surge, distance/time-based)
- Design trip lifecycle and historical trip tracking
- Account for map integration and routing services
12. Design a Food Delivery App
- Model users, restaurants, menus, orders, and delivery partners
- Handle real-time status tracking (order received, prepared, out for delivery)
- Match orders with nearby delivery agents based on ETA
- Include payment processing and delivery rating
- Consider multi-tenancy (thousands of restaurants and orders)
13. Design an Online Auction System
- Design auctions, bidders, bids, timers, and product listings
- Handle real-time updates for current highest bids
- Manage concurrency for simultaneous bids
- Support time-based auction expiration
- Design winner selection and payment post-auction
14. Design a Scalable Chat Application
- Model users, messages, conversations (1–1 and group)
- Store chat history with pagination and search
- Support online/offline presence, delivery status, and read receipts
- Allow media/file attachments
- Include end-to-end encryption as an optional discussion
15. Design a Collaborative Document Editor
- Model document, user session, and version control
- Support concurrent editing (using CRDTs or Operational Transforms)
- Maintain access permissions (read-only, edit, comment)
- Auto-save and history/version comparison
- Integrate real-time cursor and edit indicators
16. Design a Stock Trading Platform
- Model orders (limit/market), order book, users, and trades
- Design matching engine with FIFO/LIFO strategies
- Real-time price broadcasting to users
- Handle trading rules and time windows
- Discuss reliability and concurrency at scale
17. Design a News Feed System
- Model users, posts, comments, and relationships (followers)
- Feed generation using pull/push or hybrid model
- Personalization logic using user behavior or preferences
- Support infinite scroll and pagination
- Cache hot or trending posts for performance
18. Design a Hotel Booking System
- Model hotels, rooms, bookings, locations, and filters
- Implement availability checking and locking for room selection
- Support cancellations and refunds
- Add payment and invoice handling
- Ensure consistency under concurrent booking scenarios
19. Design a Personalized Content Recommender (GenAI-enhanced)
- Represent users, preferences, content, and interaction history
- Use collaborative filtering or content-based filtering as a base
- Integrate GenAI for personalization and dynamic content generation
- Store embeddings and use vector similarity for recommendations
- Track and learn from user feedback to improve suggestions
20. Design an Interview Prep Chatbot
- Define question banks, chat context, and session management
- Integrate LLM for generating tailored answers
- Support multi-turn conversation flow
- Include fallback responses for irrelevant inputs
- Allow feedback and learning mechanism for better answers
21. Design an AI-Based Customer Support System
- Create a ticket management backend
- Integrate LLM for initial response and classification
- Enable agent handoff for complex queries
- Store conversation history and escalation paths
- Use user sentiment analysis to prioritize
22. Design a Smart Email Auto-Responder
- Connect to email client and parse context of incoming mail
- Use LLM to generate reply templates dynamically
- Learn tone and preferences from previous replies
- Include manual override and review before send
- Track accuracy of responses over time for feedback
23. Design a Document Search System using RAG
- Index documents using traditional + vector embeddings
- Retrieve relevant chunks using similarity search
- Pass chunks to LLM for answer generation
- Model documents, chunks, metadata, and retrieval flow
- Optimize for latency and relevance
24. Design a Resume Parser and Job Matcher
- Parse resume fields using NLP (name, skills, experience, etc.)
- Model job descriptions and tag required fields
- Use LLM for semantic similarity scoring
- Support filtering, ranking, and suggestions
- Allow real-time updates as resumes or JDs change
25. Design an Intelligent Code Review Bot
- Integrate with GitHub/GitLab CI pipelines
- Use AST parsing and LLM to generate suggestions
- Comment on code quality, style violations, and performance
- Include confidence score per suggestion
- Enable developer feedback for model improvement
26. Design an API Rate Limiter with Redis
- Track request counts per user/IP with TTLs
- Implement fixed window or sliding log logic
- Use Redis atomic operations and expiry
- Handle global vs per-endpoint rate limits
- Ensure thread safety in distributed environments
27. Design a Watch History Tracker
- Model video sessions, playbacks, and user profiles
- Track watch progress per video and resume capability
- Include history deletion and privacy controls
- Sync across devices and user sessions
- Extend to recommendation use cases
28. Design a Task Scheduler
- Manage job definitions, triggers, and executions
- Support delayed, recurring, and one-time tasks
- Retry mechanism with exponential backoff
- Log outcomes and notify failures
- Design for distributed workers and high availability
29. Design an Audit Logging System
- Model log events with metadata (who, what, when, where)
- Write logs in immutable format and store securely
- Support log filtering, searching, and archiving
- Define retention policies and data lifecycle
- Ensure logs cannot be tampered with (compliance)
30. Design a Request Tracing System
- Generate and propagate trace IDs across services
- Collect timing and call stack details in a trace store
- Visualize trace graphs to detect latency bottlenecks
- Support sampling and filtering of trace data
- Integrate with existing observability stack (e.g., OpenTelemetry)
