Performance Testing

Measure response time per request, throughput as requests per second, error rate as the percentage that fail, and latency percentiles p50, p95, and p99, and judge against percentiles rather than the average because the average hides the slow tail that real users feel.

Performance testing measures how a system behaves under load, using load testing for normal demand, stress testing to find the breaking point, spike testing for sudden bursts, and endurance or soak testing for sustained load that reveals leaks over time.

JMeter is the mature GUI-based open-source standard, Gatling is code-based in Scala with great reports, k6 is JavaScript-based and CI/CD-friendly, and Locust is Python-based, and you choose by team skills, scripting versus GUI, reporting, and pipeline fit.