DSA & System Design

System design · Playground

Design it, then break it

6 challenges, graded on the decisions interviewers look for. New to this? Start with a guided mission and a coach beside you.

  • 6 challenges
  • 41 graded checks
  1. 1Read the briefRequirements and rough numbers, like the first five minutes of an interview.
  2. 2Build itDrag components onto the canvas and wire them together. A live checklist shows what your design is missing.
  3. 3Break itSimulate traffic, spike it ten times, kill a component, and see where it gives.
  • 7 checks

    URL shortener

    Design a service that turns long URLs into 7-character codes and redirects fast.

    • Create short links and redirect
    • Reads outnumber writes 100:1
    • Count clicks without slowing redirects
    Guided mission · 5 stepsFree challenge
  • 6 checks

    Rate limiter

    Add a distributed rate limiter in front of an API so every client gets a fair share.

    • Limit each API key, e.g. 100 requests/minute
    • Consistent across many gateway instances
    • Under 5 ms added latency
    Guided mission · 4 stepsFree challenge Pairs with the Rate Limiter question
  • 7 checks

    Notification system

    Send push, email and SMS notifications reliably, without duplicates, honouring user preferences.

    • Multiple channels with per-user preferences
    • No duplicates; retries are safe
    • A slow SMS provider must not block push
    Start the challenge
  • 7 checks

    Real-time chat

    Design 1:1 and group chat with delivery receipts, offline delivery and history.

    • Messages delivered in real time to online users
    • Offline users get a push and catch up later
    • Message history is durable
    Start the challenge Pairs with the Real-Time Chat App question
  • 7 checks

    News feed

    Design a home feed for 300M daily users, including celebrities with millions of followers.

    • Feed loads in under 200 ms
    • New posts reach followers within seconds
    • Celebrity posts don't explode write cost
    Start the challenge Pairs with the News Feed (Twitter or Instagram) question
  • 7 checks

    Ticket booking

    Sell seats for a blockbuster launch without ever double-booking a seat.

    • Hold seats for 5 minutes while paying
    • Never double-book
    • Live seat maps
    Start the challenge Pairs with the Movie Ticket Booking question
  • Free canvas

    Sandbox

    No brief and no grade. Start from a lesson or case-study diagram, change it, and watch the simulator react.

    Open the sandbox