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name: web-performance-audit description: Web performance audits with Core Web Vitals, bottleneck identification, optimization recommendations. Use for page load times, performance reviews, UX optimization, or encountering LCP, FID, CLS issues, resource blocking, render delays. license: MIT

Web Performance Audit

Conduct comprehensive performance audits and implement optimizations.

Core Web Vitals Targets

Metric	Good	Needs Improvement	Poor
LCP (Largest Contentful Paint)	<2.5s	2.5-4s	>4s
FID (First Input Delay)	<100ms	100-300ms	>300ms
CLS (Cumulative Layout Shift)	<0.1	0.1-0.25	>0.25
INP (Interaction to Next Paint)	<200ms	200-500ms	>500ms

Performance Measurement

// Using web-vitals library
import { getCLS, getFID, getLCP, getTTFB } from 'web-vitals';

function sendToAnalytics({ name, value, id }) {
  console.log({ name, value, id });
}

getCLS(sendToAnalytics);
getFID(sendToAnalytics);
getLCP(sendToAnalytics);
getTTFB(sendToAnalytics);

Lighthouse Automation

const lighthouse = require('lighthouse');
const chromeLauncher = require('chrome-launcher');

async function runAudit(url) {
  const chrome = await chromeLauncher.launch({ chromeFlags: ['--headless'] });
  const result = await lighthouse(url, {
    port: chrome.port,
    onlyCategories: ['performance']
  });

  await chrome.kill();
  return result.lhr;
}

Optimization Strategies

Quick Wins (1-2 days)

• Enable gzip/brotli compression
• Minify CSS/JS
• Defer non-critical scripts
• Optimize images (WebP, lazy loading)

Medium Effort (1-2 weeks)

• Implement code splitting
• Add service worker caching
• Preload critical resources
• Eliminate render-blocking resources

Long-term (1-3 months)

• Architecture improvements
• CDN optimization
• Database query optimization

Performance Budget

{
  "timings": [
    { "metric": "first-contentful-paint", "budget": 1500 },
    { "metric": "largest-contentful-paint", "budget": 2500 }
  ],
  "resourceSizes": [
    { "resourceType": "script", "budget": 150 },
    { "resourceType": "image", "budget": 300 }
  ]
}

Audit Checklist

• Measure baseline Core Web Vitals
• Run Lighthouse audit (mobile & desktop)
• Analyze real user metrics (RUM)
• Identify largest contentful element
• Check for layout shifts
• Review JavaScript bundle size
• Test on slow 3G connection
• Set performance budget
• Configure monitoring alerts