I kept watching engineers freeze in system design interviews, so I built a practice tool

#systemdesign #webdev #career #interview

I've interviewed a lot of engineers for system design rounds over the years. The pattern that kept bugging me: candidates clearly understood the theory but fell apart when they had to actually build something from scratch.

They'd watched all the YouTube videos. Memorized the classic walkthroughs. But give them a slightly different problem and they'd freeze.

Same thing when friends asked me to help them prep. We'd jump on a call, I'd give them a prompt, and they'd stare at the screen not knowing where to start. The problem was never that they didn't know what a load balancer does — it's that they'd never practiced going from a blank page to a full architecture while tracking requirements and defending choices out loud.

And when I wasn't around to run the mock? They had no way to get feedback. You can practice drawing diagrams all day, but without someone pushing back on your decisions and asking "what happens when this fails?" — you're just reinforcing your own blind spots.

So I built Supaboard.

What it is

A visual whiteboard purpose-built for system design. Not a general diagramming tool — every feature exists because system design interviews need it:

Pre-built components: Databases, caches, queues, load balancers, CDNs, servers, clients. Drag and drop, not draw-from-scratch.
Requirements tracker: A floating checklist that mirrors how interviewers actually score you. Track functional and non-functional requirements as you build.
Community gallery: Browse real architecture diagrams from other engineers. See how others approach the same problem differently.

What's new: Challenges + AI Mentor

These two features are what I'm most excited about.

Challenges give you a real prompt with requirements baked in — the kind of thing I'd give someone in a mock interview. Instead of staring at a blank canvas, you get a structured starting point.

AI Mentor looks at your actual diagram and asks hard questions about tradeoffs and failure scenarios. It's basically the feedback part of a mock interview, available anytime — not just when a senior engineer friend has 45 minutes to spare.

The combination means you can run a full practice session solo: pick a challenge, build the architecture, get pushed on your blind spots, iterate.

The stack (for the nerds)

Next.js 16 + React 19
tldraw v4 for the canvas
Supabase for auth + database
Stripe for billing
Tailwind v4 + shadcn/ui
Deployed on Vercel

Why not just use Excalidraw?

Excalidraw is great for general diagramming. But for system design specifically, the gaps are real:

No pre-built system components — you're labeling rectangles
No requirements tracking — you forget half the constraints mid-diagram
No community — you draw in isolation with no feedback loop
No feedback mechanism — you don't know what you're missing until the actual interview

Supaboard exists because I kept seeing the same failure mode: smart engineers who knew the concepts but never had a way to practice the full loop of building + defending an architecture.