System Design Diagrams#
120 system designs. Each topic comes with three Markdown files, all rendered with mermaid:
- Simple — the 30-second mental model. The boxes and arrows you'd draw on a whiteboard.
- Detailed — the production-grade view: every microservice, queue, cache, and failure mode, plus a glossary of fundamentals it touches.
- Notes — requirements, capacity estimation, API surface, schema, trade-offs, and references.
Tip: click ☆ Bookmark next to any heading to save a page; the floating ★ panel in the bottom-right opens your full list. Bookmarks live in your browser only — nothing is synced.
How the catalogue is organised#
12 tiers, each tab at the top of the page:
| Tier | Tag | What it covers | Examples |
|---|---|---|---|
| HLD Fundamentals | HLD |
Distributed-systems building blocks reused across every design | Load balancer, CDN, consistent hashing, LSM/B-tree, CRDTs, sagas, observability |
| LLD Concepts | LLD |
Object-oriented design + concurrency primitives | SOLID, design patterns (creational / structural / behavioural), DI, mutexes, deadlocks, immutability |
| Classics | HLD |
The canonical interview set | URL shortener, rate limiter, Snowflake ID, web crawler, key-value store |
| Social & Communication | HLD |
Feeds, chat, presence | Twitter, Instagram, WhatsApp, Slack, LinkedIn, TikTok |
| Media & Streaming | HLD |
Upload pipelines, ABR, live | YouTube, Netflix, Spotify, Twitch, Zoom, Reels |
| Storage & File | HLD |
Sync, object stores, distributed FS | Google Drive, Google Photos, S3, GFS/HDFS, MongoDB, TSDB |
| E-commerce & Marketplaces | HLD |
Catalog, cart, order, fulfilment | Amazon, Flipkart, eBay auction, DoorDash, Ticketmaster, Airbnb |
| Location & Maps | HLD |
Geo indexing, dispatch, proximity | Google Maps, Uber, Yelp, Find My Friends, geofencing |
| Financial & Payments | HLD |
Ledgers, rails, fraud | Stripe-like gateway, digital wallet, UPI, exchanges, fraud detection, Splitwise |
| Infrastructure & Platform | HLD |
The 20 platform pieces every backend leans on | Kafka, search engine, recommendation, ad aggregation, feature flags, DNS, distributed lock |
| Real-time Collaboration | HLD |
OT, CRDTs, multiplayer canvases | Google Docs, Figma, Notion, whiteboard, live-share editors |
| Specialised / Niche | HLD |
Domain-specific systems | Game server, matchmaking, code execution sandbox, voting, calendar, OAuth |
| LLD-flavoured | LLD |
Interview-popular OO designs | Parking lot, elevator, ATM, chess, hotel, logger |
The left sidebar drills from tier → topic → Simple/Detailed/Notes. Search (top right or press /) covers every page including diagram labels.
Suggested reading paths#
- Brand new to system design — start with Fundamentals → Load balancer, CDN, Caching strategies, Database sharding, CAP/PACELC. Then move into Classics.
- Interview prep, Tier-1 must-knows — URL shortener, Rate limiter, Snowflake ID, News feed, Search autocomplete, Key-value store.
- You already know the basics — pick a tier from the top tabs and walk Simple → Detailed → Notes for any topic.
How to read a topic#
Every topic folder has the same three files in this order:
simple.md— open this first. One mermaid block, a handful of boxes, the mental model you want to be able to redraw under interview pressure.notes.md— read this second. Requirements, capacity estimates, API, schema, trade-offs, references. Skim in 3 minutes; re-derive the simple diagram from it.detailed.md— open this last. Full production view with every component you'd be asked about. A Glossary & fundamentals appendix links to the fundamentals pages each concept builds on.
Diagram conventions#
- Clients left, storage right, services in the middle.
- Solid arrow
→= synchronous request; dashed arrow-.->= async (queue, event). - Subgraphs group logical tiers (edge, app, data, async, observability).
- Click any diagram to open the full-screen viewer (zoom + pan + fullscreen + copy mermaid source).
- The colour palette + shape language is consistent across every page and works on both light and dark themes:
| Component | Colour | Shape | Examples |
|---|---|---|---|
| Client / user | 🟦 blue | stadium ([…]) |
Browser, mobile app, partner API |
| Edge | 🟦 cyan | hexagon {{…}} |
DNS, CDN, LB, API gateway, WAF |
| Service | 🟨 amber | rectangle […] |
Microservice, business logic, API tier |
| Compute / async | 🟩 green | stadium ([…]) |
Workers, transcoders, schedulers, ML inference |
| Cache | 🟧 orange | cylinder [(…)] |
Redis, Memcached, in-process cache |
| Datastore | 🟥 red | cylinder [(…)] |
SQL, NoSQL, KV, doc DB, time-series |
| Storage | ⬜ grey | cylinder [(…)] |
S3, GCS, object/blob, archive |
| Queue / stream | 🟪 purple | subroutine [[…]] |
Kafka, SQS, pub/sub, outbox |
| External (3rd party) | 🟪 pink | circle ((…)) |
Stripe, Twilio, APNS/FCM |
| Observability | 🟪 violet | flag >…] |
Metrics, logs, traces, alerts |
Scaling cues: a label suffix × N means horizontally scaled (e.g. App pod × N). ↑ scale up denotes vertical scale-up. (primary) / (standby) for active-passive pairs. See authoring rules for the full convention.
Sources#
Designs are synthesised from widely-circulated public material: Alex Xu's System Design Interview Vol 1 & 2, Grokking the System Design Interview, ByteByteGo, Designing Data-Intensive Applications, AWS/GCP/Azure architecture blogs, the High Scalability site, and engineering blogs of the companies whose systems are being modelled.
Status#
| Tier | Done |
|---|---|
| Fundamentals | 20 / 20 |
| Classics | 10 / 10 |
| Social & Communication | 10 / 10 |
| Media & Streaming | 6 / 6 |
| Storage & File | 6 / 6 |
| E-commerce & Marketplaces | 7 / 7 |
| Location & Maps | 6 / 6 |
| Financial & Payments | 7 / 7 |
| Infrastructure & Platform | 20 / 20 |
| Real-time Collaboration | 5 / 5 |
| Specialised / Niche | 13 / 13 |
| LLD-flavoured | 10 / 10 |
| Total | 120 / 120 |