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core-web-vitals

Skill0 starsChanged 3 months agoMITView on GitHub

Use when diagnosing or optimizing LCP, INP, CLS — Core Web Vitals at the 75th percentile (LCP ≤2.5s, INP ≤200ms, CLS ≤0.1).

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SKILL.md

Core Web Vitals

Measured LCP/INP/CLS diagnosis. From addyosmani/web-quality-skills core-web-vitals.

When to use

  • LCP, INP, or CLS fail thresholds
  • User says "improve Core Web Vitals", "fix LCP", "reduce CLS"

Workflow

  1. Measure — Capture field (CrUX) + lab (Lighthouse, trace) at 75th percentile for LCP, INP, CLS.
  2. Diagnose — For the failing metric:
    • LCP: critical rendering path, server response, render-blocking, image priority
    • INP: long tasks, main-thread blocking, hydration cost
    • CLS: layout shifts, font swapping, late-injected content
  3. Optimize — One metric at a time, keep failures separate from hypotheses (see performance audit).
  4. Verify — Re-measure at p75; confirm thresholds, no regression on other metrics.

Verification

  • Baseline at p75 recorded for the failing metric
  • Diagnosis maps to metric-specific cause, not generic optimization
  • Fix applied to single metric, re-measured, thresholds met

References

  • Source: addyosmani/web-quality-skills core-web-vitals

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