Learn
System Design
Design problems worked end to end: requirements, back-of-envelope numbers, the architecture, and the trade-offs an interviewer will push on.
Articles32
Design a Collaborative Editor (LLD)
4 minThe transform function, worked through concretely — and why CRDTs make character identity the answer instead.
Design a Dating App (LLD)
4 minA filter chain for eligibility, a canonical match key, and the safety rules that belong in the domain model.
Design a Distributed Message Queue
4 minA partitioned append-only log with consumer-managed offsets — plus what each delivery guarantee actually costs.
Design a Food Delivery App (LLD)
3 minThree actors, one order state machine, and a pricing pipeline that composes instead of branching.
Design a Hotel Booking System
4 minInventory per room-type per night, and the concurrency control that stops two people buying the last room.
Design a Key-Value Store
4 minConsistent hashing, quorum replication, and the CAP trade-off made concrete — the foundational distributed systems question.
Design a Music Streaming Service (LLD)
4 minA player state machine plus a queue whose shuffle and repeat behaviours are strategies, not flags.
Design a News Feed System
4 minFanout on write, fanout on read, and the hybrid that handles celebrities — the core trade-off in social system design.
Design a Notification Engine (LLD)
4 minOne request, many channels — strategy for delivery, a preference layer, and idempotent retries.
Design a Payment Gateway (LLD)
4 minIdempotency keys, an explicit state machine and a double-entry ledger — the three things money systems cannot do without.
Design a Quick Commerce App (LLD)
4 minDark stores, reserved inventory and a 10-minute clock — the constraint that makes this different from food delivery.
Design a Rate Limiter
4 minToken bucket in Redis, atomic counters, and the distributed-state problem that makes this question interesting.
Design a Stock Exchange
4 minA single-threaded matching engine over an in-memory order book — the one design where sharding is the wrong answer.
Design a Web Crawler
4 minThe URL frontier is the whole design — priority for what to crawl next, politeness for not overwhelming any host.
Design ChatGPT
4 minGPU capacity is the scarce resource — continuous batching, KV caching and streaming are how you spend it well.
Design Chess (LLD)
4 minPolymorphic pieces, two-phase move validation, and the special rules that expose whether your model is real.
Design Google Docs
4 minA session server per document holding the authoritative state — plus OT or CRDTs to reconcile concurrent edits.
Design Google Drive
3 minContent-addressed chunks give dedup and delta sync for free — the metadata service is where the real design lives.
Design Google Maps
4 minPre-rendered tiles, a partitioned road graph with precomputed shortcuts, and live traffic folded into edge weights.
Design Instagram
3 minPhoto pipeline into blob storage and a CDN, hybrid feed fanout, and stories as TTL'd content.
Design LeetCode
3 minThe hard part is running untrusted code safely — everything else is a queue and a leaderboard.
Design Netflix
4 minA finite catalogue encoded once and pushed to CDN appliances inside ISPs — the opposite problem to YouTube.
Design Reddit
4 minTime-decayed ranking, nested comment trees with materialised paths, and vote counters that survive a viral post.
Design Snake and Ladder (LLD)
3 minSnakes and ladders are the same thing — one Jump abstraction, one lookup map, and the design collapses.
Design Tic Tac Toe (LLD)
3 minThe warm-up machine-coding round — judged on the O(1) win check and whether your design generalises to N×N.
Design TikTok
4 minA feed built from a recommendation model rather than a follow graph — which inverts the usual social design.
Design Tinder
4 minPrecomputed candidate decks, a swipe store optimised for one query, and atomic mutual-match detection.
Design TinyURL
4 minBase62 over a distributed counter, a cache in front of a key-value store, and the 301-vs-302 decision.
Design Twitter
3 minTimeline fanout with a celebrity carve-out, a sharded tweet store, and streaming trends.
Design Uber
4 minHigh-frequency location writes, cell-based proximity search, and a matching loop that must not double-assign a driver.
Design WhatsApp
4 minPersistent connections plus a session registry, an inbox per user, and the three-tick delivery state machine.
Design YouTube
3 minChunked upload, a parallel transcoding pipeline, adaptive bitrate over a CDN — and why the CDN is the system.
Topics32
Every topic on the System Design sheet, in the order the sheet works through them. 32 of 32 have a written guide so far — the rest link straight to their questions on the sheet.
- Design a Rate LimiterGuide
- Design TinyURLGuide
- Design TwitterGuide
- Design YouTubeGuide
- Design Google DriveGuide
- Design Google MapsGuide
- Design a Key-Value StoreGuide
- Design a Distributed Message QueueGuide
- Design a News Feed SystemGuide
- Design Stock Exchange SystemGuide
- Design Google DocsGuide
- Design a Web CrawlerGuide
- Design TinderGuide
- Design ChatGPT SystemGuide
- Design a Hotel Booking SystemGuide
- Design NetflixGuide
- Design RedditGuide
- Design UberGuide
- Design WhatsAppGuide
- Design LeetCodeGuide
- Design InstagramGuide
- Design TikTokGuide
- Design Google Docs (Collaborative Editor)Guide
- Design Food Delivery App (Zomato / Swiggy)Guide
- Design Notification EngineGuide
- Design Music Streaming Service (Spotify)Guide
- Design Payment Gateway SystemGuide
- Design Quick Commerce App (Zepto / Blinkit)Guide
- Design Dating App (Tinder)Guide
- Design Tic Tac Toe GameGuide
- Design Snake and Ladder GameGuide
- Design Chess GameGuide
Related
System Design sheet
Practise the topics above and track what you have solved.
DSA Patterns articles
The recurring shapes behind interview problems — what each pattern is, when it applies, the template that solves it, and the mistakes that cost people the round.
SQL articles
Query topics as they actually come up in interviews — joins, window functions, CTEs and the analytics patterns built on them, each with runnable queries.