Get 'Senior Engineer' level feedback on your system design. Submit your architecture diagram and component choices for any use case (e.g., Uber-like tracking, TikTok feed, CDC pipelines). I will identify Single Points of Failure (SPOF), suggest better tool choices (Kinesis vs. Kafka, SQL vs. NoSQL), and explain the trade-offs. This is the closest you can get to a mock interview without the live pressure.