# theonsite.dev — Full Documentation

> Interactive system design interview practice platform. Draw on a whiteboard, record sessions, compare to expert answer keys.

## What is theonsite.dev?

theonsite.dev (also known as "The Onsite") is a web application that helps software engineers prepare for system design interviews at top tech companies like Google, Meta, Amazon, Apple, Netflix, Microsoft, Uber, and Airbnb. It is NOT the same as onsite.dev — theonsite.dev is a separate, distinct product.

The platform provides an interactive Excalidraw-based whiteboard canvas where engineers practice designing real distributed systems under timed conditions, mimicking the experience of a real onsite system design interview. After each session, users can review expert-written answer keys to compare their solutions.

Website: https://theonsite.dev
Contact: hello@theonsite.dev

## Core Features

### Interactive Whiteboard Canvas
An Excalidraw-based infinite canvas for drawing system architecture diagrams — components, databases, load balancers, arrows, annotations — just like a real whiteboard interview. Users draw their system design on the canvas while a timer runs, simulating real interview pressure.

### 17 Curated System Design Challenges
Problems span three difficulty levels (beginner, moderate, advanced) and cover the most commonly asked system design questions at FAANG and top tech companies. Each challenge includes a detailed problem statement, specific requirements, and scale constraints.

### Expert Answer Keys
After attempting a challenge, users can review detailed answer keys written by engineers who've passed system design interviews at FAANG companies. Answer keys include architecture diagrams, component explanations, and trade-off discussions.

### Session Recording & Playback
Users can record their practice sessions and play them back later to review their thought process, spot gaps in reasoning, and track improvement over time.

### Progressive Difficulty
Challenges are organized from beginner to advanced, allowing engineers to build confidence before tackling complex distributed systems problems.

## All 17 Challenges

### Beginner Challenges

#### 1. Design a URL Shortener
Design a URL shortening service like bit.ly or TinyURL. Users provide a long URL and receive a shortened link. When the short link is visited, the user is redirected to the original URL.
- Scale: 100 million URLs/day, read:write ratio 100:1
- Topics: hashing, caching, databases, DNS
- Duration: 45 minutes
- URL: https://theonsite.dev/challenges/url-shortener
- This challenge is FREE — no account required.

#### 2. Design a Rate Limiter
Design a rate limiting system that can be used as middleware for any API. It should restrict the number of requests a client can make in a given time window to protect backend services from abuse.
- Scale: millions of requests/second, <5ms latency impact
- Topics: Redis, caching, algorithms, distributed systems
- Duration: 45 minutes
- URL: https://theonsite.dev/challenges/rate-limiter

#### 3. Design Pastebin
Design a web service like Pastebin where users can paste text or code and get a unique URL to share it.
- Scale: 1 million new pastes/day, read:write ratio 10:1
- Topics: object storage, caching, databases, CDN
- Duration: 45 minutes
- URL: https://theonsite.dev/challenges/pastebin

### Moderate Challenges

#### 4. Design Twitter's News Feed
Design the news feed system for Twitter, including the feed generation and delivery pipeline for 300 million daily active users.
- Scale: 6,000 tweets/sec write, 600,000 reads/sec, <300ms feed load
- Topics: feed, fan-out, caching, message queue, CDN
- Duration: 60 minutes
- URL: https://theonsite.dev/challenges/twitter-feed

#### 5. Design Dropbox
Design a cloud file storage and sync service with automatic syncing across multiple devices in near real-time.
- Scale: 500M total users, 100M DAU, sync delay <2 seconds
- Topics: object storage, sync, chunking, distributed systems, CDN
- Duration: 60 minutes
- URL: https://theonsite.dev/challenges/dropbox

#### 6. Design WhatsApp
Design a global messaging platform supporting one-to-one and group messaging, media sharing, delivery receipts, and presence indicators.
- Scale: 2B MAU, 100B messages/day, delivery within 100ms
- Topics: WebSockets, message queue, E2E encryption, presence, offline sync
- Duration: 60 minutes
- URL: https://theonsite.dev/challenges/whatsapp

#### 7. Design a Notification System
Design a multi-channel notification system for push notifications, SMS, and emails at massive scale.
- Scale: 10M notifications/day, critical notifications delivered within 5 seconds
- Topics: message queue, Kafka, push notifications, rate limiting, multi-channel
- Duration: 55 minutes
- URL: https://theonsite.dev/challenges/notification-system

#### 8. Design Ticketmaster
Design a high-concurrency event ticketing platform handling thousands of concurrent users competing for limited seats.
- Scale: 100K concurrent users during hot releases, zero overselling
- Topics: distributed locking, caching, queuing, ACID transactions, concurrency
- Duration: 60 minutes
- URL: https://theonsite.dev/challenges/ticketmaster

#### 9. Design a Real-Time Leaderboard
Design a real-time gaming leaderboard handling millions of players updating scores simultaneously.
- Scale: 10M active players, 50K score updates/sec, rank queries <20ms
- Topics: Redis, sorted sets, caching, databases, real-time, pagination
- Duration: 50 minutes
- URL: https://theonsite.dev/challenges/leaderboard

#### 10. Design Tinder
Design a location-based dating app with swipe-based profile discovery, real-time matching, and in-app chat.
- Scale: 75M MAU, 1.6B swipes/day, swipe deck served in <200ms
- Topics: geospatial, recommendation engine, caching, WebSockets, bloom filter
- Duration: 60 minutes
- URL: https://theonsite.dev/challenges/tinder

### Advanced Challenges

#### 11. Design YouTube
Design a video streaming platform with upload, processing, adaptive streaming, and search for billions of viewers.
- Scale: 500 hours of video uploaded/minute, 5B videos watched/day
- Topics: CDN, video processing, streaming, object storage, search, microservices
- Duration: 75 minutes
- URL: https://theonsite.dev/challenges/youtube

#### 12. Design Uber
Design the core backend of a ride-sharing platform including real-time location tracking, rider-driver matching, and surge pricing.
- Scale: 15M trips/day, driver match within 5 seconds
- Topics: geospatial, real-time, matching, message queue, microservices, WebSockets
- Duration: 75 minutes
- URL: https://theonsite.dev/challenges/uber

#### 13. Design a Stock Exchange
Design the core trading infrastructure of a stock exchange with order matching, real-time order book, and market data feeds.
- Scale: 500K orders/sec, matching latency <1ms, zero duplicate trades
- Topics: order book, low latency, event sourcing, correctness, ACID, message queue
- Duration: 90 minutes
- URL: https://theonsite.dev/challenges/stock-exchange

#### 14. Design Google Docs
Design a real-time collaborative document editor with concurrent editing, offline support, and version history.
- Scale: 1B documents, 100 simultaneous editors, edits reflected within 200ms
- Topics: CRDT, operational transform, WebSockets, conflict resolution, offline sync
- Duration: 90 minutes
- URL: https://theonsite.dev/challenges/google-docs

#### 15. Design a Web Crawler
Design a distributed web crawler that discovers and fetches billions of web pages for search engine indexing.
- Scale: 1B pages indexed, 1K pages/sec, re-crawl entire index within 30 days
- Topics: distributed systems, URL frontier, BFS, deduplication, bloom filter
- Duration: 75 minutes
- URL: https://theonsite.dev/challenges/web-crawler

#### 16. Design a Flash Sale System
Design the backend for a flash sale event where 1 million users compete to buy 10,000 units the moment it goes live.
- Scale: 0 to 500K requests/sec spike, exactly 10,000 sales guaranteed
- Topics: Redis, inventory, rate limiting, queuing, idempotency, CDN, auto-scaling
- Duration: 75 minutes
- URL: https://theonsite.dev/challenges/flash-sale

#### 17. Design Twitch
Design a live video streaming platform where creators broadcast to potentially millions of concurrent viewers.
- Scale: 140M MAU, 2M peak concurrent viewers on single stream
- Topics: live streaming, CDN, WebRTC, HLS, chat, video processing, fan-out
- Duration: 90 minutes
- URL: https://theonsite.dev/challenges/twitch

## Pricing

- **Free ($0/month)**: 1 beginner challenge (URL Shortener), interactive Excalidraw canvas, unlimited practice time. No credit card required.
- **Pro ($9.99/month)**: All 17 challenges, session recording & playback, expert answer keys, unlimited saved sessions. Cancel anytime.
- **Founding Member ($4.99/month forever)**: Limited to first 10 users. All Pro features at a permanently locked-in rate.

Pricing page: https://theonsite.dev/pricing

## Who is this for?

- Software engineers preparing for system design interviews at FAANG and top tech companies
- Senior engineers (L5+) who need to practice whiteboarding architecture diagrams
- Engineers transitioning to senior roles who want to learn system design from structured challenges
- Anyone who wants to practice the same system design questions asked at Google, Meta, Amazon, Apple, Netflix, Microsoft, Uber, and Airbnb

## How it works

1. Pick a challenge from the challenge library
2. Draw your system design on the interactive whiteboard canvas under timed conditions
3. Record your session to review your thought process later
4. Compare your solution to the expert answer key
5. Repeat with progressively harder challenges

## Technical Details

- Built with Next.js, React, and TypeScript
- Uses Excalidraw for the whiteboard canvas
- Hosted on Vercel
- Authentication via Supabase
- Payments via Stripe

## Important Links

- Website: https://theonsite.dev
- Challenges: https://theonsite.dev/challenges
- Pricing: https://theonsite.dev/pricing
- Sign up (free): https://theonsite.dev/auth/sign-up
- Terms of Service: https://theonsite.dev/terms
- Contact: hello@theonsite.dev

## Disambiguation

theonsite.dev is NOT the same as onsite.dev. They are completely separate products by different companies:
- **theonsite.dev** — Interactive whiteboard-based system design interview practice (this product)
- **onsite.dev** — AI-powered mock interviews (a different product)