Meta System Design Questions

Design an Online Judge and Live Comments

Design an online coding platform like LeetCode or Codeforces. Users browse problems, write code in the browser in many languages, submit it, and get a verdict (accepted, wrong answer, TLE, runtime error) after it runs against…

Also reported as: Design a Coding Contest Platform · Design an Online Coding Judge · Design an online coding contest platform +2 more

Design Boolean Search over User Status Posts

Design a search service over social media status posts (like Facebook post search). Users enter one or more keywords, optionally with boolean expressions (AND/OR, parentheses, precedence), and get matching posts ranked by recency…

Also reported as: Design Boolean Search for Status Posts · Design Search And Web Crawling Systems · Design a Scalable Post, Feed, and Search Service +1 more

Design an ad click aggregation service

Design an ad click and impression aggregation system. Ingest a high-volume stream of ad events ({ad_id, campaign_id, user_id, event_type, timestamp}, billions per day) and provide aggregated metrics (clicks, impressions, CTR per…

Also reported as: Design ad click tracking and dashboard at scale · Design an ad click tracking system · Design a real-time ad impression aggregator

Design Top-K, Crawler, and Chess Systems

Design a system that continuously computes the top K items from a very large event stream: for example the K most-viewed URLs, the K services with the most error logs in the last 5 minutes, the top 100 most active users in a…

Also reported as: Design a Real-Time Trending Hashtags System · Design a Top-K trending items service

Design Top-K, Crawler, and Chess Systems

Design an online chess service like chess.com. Users are matched with opponents of similar skill (rated and unrated), play real-time games with low-latency moves, and see authoritative server-managed clocks. Games end by…

Also reported as: Design an online chess platform · Design an online chess game with undo and leaderboard

Design an Instagram-Style Social Feed

Design the home feed of a social network like Instagram or Twitter. Users create posts (text, photos, video), follow other users, and open a personalized feed of recent posts from people they follow, possibly mixed with global or…

Also reported as: Design an Instagram-like platform · Design a Scalable Post, Feed, and Search Service

Design an Online Game Leaderboard

Design a real-time leaderboard service for an online game (or for ranking drivers from reviews). Players submit score updates frequently (high write volume); users query the global top N, top N per region or friends, and their…

Also reported as: Design a real-time game leaderboard · Design a game leaderboard service

Design an Online Judge and Live Comments

Design a live comments system for live video (like Facebook Live or TikTok Live), or a synchronized comment overlay pinned to a video's timeline. Viewers post comments and all viewers of the stream see new comments within about a…

Also reported as: Design real-time live comments · Design a live video comments system

Design an online auction system

Design a real-time online auction platform like eBay, or live auctions attached to social media posts. Sellers list items with a start price and end time; buyers place bids; everyone watching sees the current highest bid and bid…

Also reported as: Design Real-Time Auctions for Social Posts · Design an Instagram-like auction platform

Design content moderation for a posting app

Design a content moderation system for a social platform that detects harmful content (e.g., posts or ads selling weapons, hate speech, nudity) in text, images and video. New content is scored at upload time with low latency;…

Also reported as: Design a system to detect weapon posts · Design a weapon-ad harmful content detection system

Design Search And Web Crawling Systems

Design a distributed web crawler that starts from seed URLs and crawls about 10 billion pages (or all images reachable from given root URLs), with periodic recrawls. It must avoid fetching the same URL twice, obey robots.txt and…

Also reported as: Design a large-scale web crawler

Design an On-Demand Delivery Platform

Design an on-demand delivery marketplace like Uber Eats, DoorDash or a 10-minute quick-commerce app (Flipkart Minutes). Customers browse nearby merchants or dark-store inventory, build a cart, place and pay for orders; merchants…

Also reported as: Design a food ordering and delivery system

Design Queue And Taxi Matching Services

Design the core of a ride-hailing platform like Uber. Riders request a ride from their location; the system finds nearby available drivers, dispatches the request, and tracks the trip in real time. Drivers report their location…

Also reported as: Design a ride-sharing system like Uber

Design a location-based radius top-K search

Design a proximity search service like Yelp or Uber Eats restaurant search. Given a user's latitude/longitude, a radius, optional text query and filters (category, rating, open now), return the top K places ranked by distance and…

Also reported as: Design a nearby places (proximity) service

Design a marketplace price tracking service

Design a price tracking service like CamelCamelCamel. Users submit product links from a large marketplace, see price history charts, and set alerts to be notified when the price drops below a threshold. The system periodically…

Also reported as: Design a price drop tracking service

Design a ticket or hotel reservation system

Design an online ticketing system like Ticketmaster. Users browse and search events, view the seat map, select specific seats and hold them for about 5 minutes while completing payment, then receive tickets. Popular events cause…

Also reported as: Design ticketing system with seat hold

Design a YouTube/Netflix video platform

Design a video platform like YouTube, Netflix or TikTok. Creators upload videos (or a catalog is ingested); videos are transcoded into multiple resolutions and bitrates; viewers stream them reliably worldwide with adaptive…

Also reported as: Design a Netflix-like video streaming service

Design a recommendation system from scratch

Design a recommendation system from scratch, for example recommending posts, games, local sports teams or weekly deals to users. Cover candidate generation (collaborative filtering, content-based, social signals, location),…

Also reported as: Design a ranking and recommendation system

Design a Reliable Notification System

Design a multi-channel notification service (push, email, SMS, in-app) that other services call to notify users. It must accept sudden bursts of millions of notifications with low acknowledgement latency, persist them durably,…

Scale a Cache or Rate Limiter Across Multiple Machines

Design a distributed rate limiter that protects APIs by limiting requests (or consumed units such as LLM billing tokens or storage quota) per user, API key, tenant, or IP. It must support configurable rules (e.g., 100…

Scale a Cache or Rate Limiter Across Multiple Machines

Design a distributed cache (like Memcached or Redis cluster) and explain how it evolves as data volume grows and it runs across many machines. Cover partitioning with consistent hashing, replication, eviction policies,…

Design a fitness tracking app

Design the backend for a fitness tracking app like Strava: users record workouts (runs, rides) with GPS routes and sensor data, view history and stats, follow friends and see their activity feed, and compete on segments or…

Design a chat messaging system

Design a real-time chat system like WhatsApp or Slack supporting one-to-one and group conversations (and, for Slack variants, workspaces, channels and threaded replies). Users send and receive messages with low latency, see…

Design a ticket or hotel reservation system

Design a hotel or rental booking system like Booking.com or Airbnb. Users search listings by location and date range with filters, view availability and a price quote, book a room or property, and cancel; hosts manage listings,…

Design a post privacy/visibility system

Design a privacy system for social media posts (like Facebook). Each post can be Public, Friends, Friends-of-friends, Only me, or Custom (allow/deny lists and groups). Privacy must be enforced everywhere posts are shown: feed,…

Troubleshoot a single-node web outage

A production service has become slow after scaling up (or a single-node web server is down). Walk through how you would diagnose the problem: which metrics, logs and traces you would check, how you would form and test hypotheses…

Design a distributed job scheduler

Design a distributed job scheduler that runs user-defined jobs at a specified time (one-time) or on a recurring cron schedule, at a scale of millions of jobs per day. Requirements: jobs fire close to their scheduled time, each…

Design versioned in-memory key-value store

Design a low-level, embeddable key-value store library using only in-memory map-like data structures. Support put, get and delete; versioned reads (get the value of a key as of version or timestamp T); snapshots and rollback to…

Design a flight search platform

Design a flight search platform like Google Flights or Kayak. Users search one-way or round-trip flights by origin, destination and dates with filters, and get results that include multi-leg itineraries sorted by price or…