Assess learners' ability to identify, measure, and analyze performance bottlenecks across frontend, backend, database, and network layers of modern web application stacks using scenario-based questions. Include interpretation of profiling outputs (Lighthouse, browser devtools, APM traces, flame graphs, SQL EXPLAIN), selection of appropriate metrics (latency, throughput, error rate, resource utilization), root-cause reasoning for contention or slowdowns, and proposing prioritized mitigation strategies with consideration of trade-offs, cost, and monitoring/alerting approaches.