z-web-performance
Installation
SKILL.md
Web performance
Diagnose and improve page-rendering performance against Core Web Vitals, using the strongest available evidence and attributing regressions to a specific change.
Metrics and thresholds
Source: web.dev/articles/vitals (Core Web Vitals), verified 2026-10-18.
| Metric | Good | Needs improvement | Poor |
|---|---|---|---|
| LCP (Largest Contentful Paint) | <= 2.5 s | 2.5 s - 4.0 s | > 4.0 s |
| INP (Interaction to Next Paint) | <= 200 ms | 200 ms - 500 ms | > 500 ms |
| CLS (Cumulative Layout Shift) | <= 0.1 | 0.1 - 0.25 | > 0.25 |
Assess each metric at the 75th percentile across page views, per device class (mobile and desktop separately).
Evidence hierarchy
Ordered strongest first for proving user experience. Use the strongest source available; state which one a claim rests on.