Live at howitscales.dev
Interactive system design you can play with. Pick a real system, press Play, and watch a request travel through it and back — then push traffic until something breaks.
Uber, Swiggy, a URL shortener and a web page load, animated component by component. Free, no account, and your own draw.io diagrams work too.
4
systems
17
guided flows
50
components
Free
no account
Why it exists
Most system design material is a static diagram and a wall of text. It tells you a cache sits in front of the database, but not what happens to the request that misses it, or which box falls over first when traffic spikes. HowItScales animates the request instead: every hop, every component, and the point where the queue starts to back up.
System design examples
Each system comes with guided flows that walk one request end to end. Click any component to see what it does and how confident the model is about it.
What you can do
Pick a system, press Play, and watch a request travel through it and back. Step through each hop at your own pace instead of squinting at a static diagram.
Turn up the load and watch queues fill, latency climb and requests get rejected. The bottleneck stops being an abstract interview answer and becomes something you can see.
Every component is labelled Documented, Assumption or Hypothetical, so you always know which parts come from public engineering write-ups and which are an educated guess.
Import a .drawio, .xml or .drawio.svg file and animate your own architecture. Files are parsed in the browser and never stored on a server.
Build a system from scratch on a canvas, animate it, then share a link or export it as JSON for a design review or a mentoring session.
No sign-up and no paywall. Code is MIT licensed and the content is CC BY 4.0, so you can reuse it in your own talks and notes.
Who it is for
Preparing for a system design interview
Explaining your architecture to a team
Learning how large systems actually work
Teaching or mentoring other engineers
New to the topic? Start with the beginner's guide to system design, or import a draw.io diagram you already have. HowItScales is not affiliated with the companies shown; simulations are educational and use adjustable assumptions, not real performance data.
Free, runs in your browser, no account needed.