Architect distributed systems. Stress-test under surge & chaos. Get objective verdicts.
HLDArena replaces hand-wavy High-Level Design (HLD) whiteboard interviews with a deterministic simulation judge. Wire load balancers, caches, queues, and sharded databases, co-compile your Markdown design spec, and watch 60 seconds of live queueing & node-crash telemetry determine your score.
Prose claims only count when the matching node and edge exist on your diagram.
Tests M/M/c saturation, Zipfian hotkey skew, primary crashes, and 8x gray brownouts.
Share verified AC topologies and unlock peer solutions after AC or 3 attempts.
How HLDArena Works — Step by Step
Click any step or simulate preset below — the Live Simulator updates right beside it in real time.
Inspect Workload Envelope, Tail-Latency SLO & Budget
Every problem gives you concrete read/write RPS, working-set memory, consistency invariants, strict p99 latency & availability gates, and a monthly cloud budget.
Hands-on experiment: Watch in the Live Simulator right beside you how 85,000 RPS against a single unsharded database breaches the 30 ms p99 SLO (TLE_LATENCY_SLO).
Easy (500) < Medium (1,000) < Hard (1,500) < Expert (2,000)
Stateless horizontal scaling, Redis read-aside caching, CDN edge offload, and basic failover.
Read-after-write guarantees, Kafka stream decoupling, inverted search indexing, and skewed bursts.
Strict serializable inventory, zero-oversell CAS locking, geo-spatial dispatch, and gray brownouts.
Celebrity hybrid fanout, Raft/Paxos leases, distributed SQL engines, and GPU token routing.
Famously Asked System Design Questions
FAANG & High-Scale Classics
Most frequently reported across LeetCode Discuss, Reddit & LinkedIn
FinTech, Inventory & Strict Locking
Zero-oversell CAS reservations, idempotency keys & ledgers
Real-Time, Geo & Live Media
High-frequency location ingestion, CRDTs & pub/sub fanout
Cloud Engines & AI Infrastructure
Distributed rate limiters, sandboxes, vector search & GPU serving
Enter the Full System Design Problemset
Filter across 15 infrastructure domains, track your Accepted progress, and benchmark latency & cloud spend.
Read Interview Loops & Verified AC Solutions
Share real L4–L7 system design experiences, debate trade-offs, and upvote high-scoring architectures.