System Design Sandbox is the interactive playground for system design interviews. Drag and drop real components (load balancers, caches, Kafka, shards, etc.), build your architecture, and get instant AI feedback that catches missing rate limiters, single points of failure, wrong consistency choices, and more with clear fixes. TinyURL scenario is live and 100% free, no signup. More scenarios drop every week. Stop drawing boxes on Excalidraw. Start practicing the way you think.