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.