Hey HN,

  I built Buildex (https://buildex.dev) to help engineers practice system design interviews interactively.
The problem: System design prep usually means reading blogs or watching videos passively. There’s no way to actually practice designing systems and get feedback.
How it works:

Pick a challenge (URL shortener, rate limiter, chat system, etc.)
Drag-and-drop components onto a canvas to design your architecture
Connect them to show data flow
Submit and get scored on efficiency, cost, and reliability
AI evaluates your design and gives specific feedback

Tech stack:

Frontend: React + Vite
Backend: Go
Database: PostgreSQL
AI: Claude API for design evaluation
Payments: Razorpay

Free tier gives you 2 AI evaluations/day. I’m a solo dev and built this over the past few months while prepping for interviews myself.
Would love feedback on:

Challenge difficulty/variety
Scoring system fairness
UI/UX issues
What’s missing?

Happy to answer any questions about the implementation.