I recently built PaperDraw.dev, a browser-based system design simulator aimed at helping engineers practice real system design thinking, not just draw static diagrams.
Most tools today are diagramming tools. They help you draw boxes and arrows, but they don’t help you answer questions like:
• What happens when traffic spikes 10×? • Where does the bottleneck appear? • How does latency propagate across services? • What breaks first under load?
That’s the gap I wanted to solve.
What it does
PaperDraw is not just a whiteboard — it’s a simulation engine for system design.
You can:
Drag and drop components like LB, Cache, DB, Queues, Services
Connect them visually
Configure throughput, latency, capacity limits
Run real-time traffic simulations
Watch bottlenecks and failures emerge
It’s essentially trying to make system design more like a flight simulator, instead of a static drawing exercise.
Why I built this
I’ve conducted and taken many system design interviews over the years, and noticed:
People memorize patterns instead of understanding trade-offs
There’s no way to experiment with architectures
Students struggle to visualize scale dynamics
So I built this as a learning + experimentation tool.
Current usage
Launched ~10 days ago:
~1k–1.5k daily users
Mostly from developers preparing for interviews
What I’d love feedback on
Does the simulation concept feel useful?
What components or scenarios should be added?
Would templates for common architectures help?
Try it here: https://paperdraw.dev
Would really appreciate your thoughts