Hey everyone,

Practicing DSA is interactive because online judges immediately tell you if you hit AC or TLE, whereas practicing High-Level Design (HLD) / System Design usually means passively reading blogs with no way to test your architecture.

So I built HLDArena: https://hldarena.vercel.app

What it does:

Draw & explain: Wire your system architecture on a whiteboard canvas and write a short plain-English HLD spec. Deterministic 60s simulation judge (zero LLM randomness): Stress-tests your design against viral traffic spikes, hotkey skew, DB crashes, p99 latency SLOs, and monthly cloud cost budgets. Objective verdicts & ratings: Gives AC, TLE, SPOF, OVER_BUDGET, etc., a scrubbable 60s telemetry replay, and a competitive rating graph across Easy → Expert HLD problems.