Performance Timeline & Timing APIs
The data source behind Core Web Vitals (LCP, FID/INP, CLS), RUM (Real User Monitoring), and performance debugging. PerformanceObserver is the modern API; the older performance.timing is deprecated.
What It Defines
Family of W3C specs for measuring browser performance: Performance Timeline (PerformanceObserver, PerformanceEntry), Navigation Timing (page load metrics), Resource Timing (per-resource fetch metrics), User Timing (custom marks and measures), and Long Tasks API.
Canonical (Normative)
Convenient (Practical)
Publishes web platform specs including CSS, accessibility, security policies, Service Workers, Web App Manifest, and many browser APIs. Also maintains some versioned HTML/DOM specs.
Related Specs
The spec behind every HTML page, form, and browser API. The canonical reference for how browsers actually parse and process HTML.
This is the core contract of every web API, browser request, and server response. You can't design or debug HTTP without knowing this.
The standard way to implement lazy loading, infinite scroll, ad viewability tracking, and scroll-triggered animations. Far more performant than scroll event listeners — runs off the main thread.