Apdex
Apdex (Application Performance Index) is a standardized metric for measuring user satisfaction with the performance of web applications and services. It calculates a score between 0 and 1 based on response time thresholds, categorizing transactions as satisfied, tolerating, or frustrated. This provides a simple, single-number summary of application performance from the user's perspective.
Developers should use Apdex when monitoring and optimizing application performance, especially for web services where user experience is critical. It helps identify performance issues by quantifying how many users are experiencing acceptable versus poor response times, making it valuable for setting service-level objectives (SLOs) and tracking improvements over time in production environments.