page-speed - SKILL.md Agent Skill

name: page-speed description: > Page speed optimization guidelines and implementation patterns. Ensures all funnel pages meet Core Web Vitals targets for LCP < 2.5s, FID < 100ms, and CLS < 0.1.

Page Speed Optimization

Every funnel page must load fast. Slow pages kill conversions — a 1-second delay reduces conversions by 7%.

Core Web Vitals Targets

Metric	Target	Impact
LCP (Largest Contentful Paint)	< 2.5s	Main content visible
FID (First Input Delay)	< 100ms	Page is interactive
CLS (Cumulative Layout Shift)	< 0.1	No visual jumping
TTFB (Time to First Byte)	< 800ms	Server responds fast

Required Optimizations

1. Critical CSS Inlining

Inline above-the-fold CSS directly in <head> to eliminate render-blocking:

<head>
  <style>
    /* Critical: hero, nav, above-fold layout only */
    .hero { /* ... */ }
    .nav { /* ... */ }
    .cta-primary { /* ... */ }
  </style>
  <!-- Defer the rest -->
  <link rel="preload" href="styles.css" as="style" onload="this.onload=null;this.rel='stylesheet'">
  <noscript><link rel="stylesheet" href="styles.css"></noscript>
</head>

2. Image Optimization

<!-- Always include width/height to prevent CLS -->
<img
  src="hero.webp"
  alt="Descriptive alt text"
  width="800"
  height="450"
  loading="lazy"
  decoding="async"
>

<!-- Responsive images with srcset -->
<img
  srcset="hero-400.webp 400w, hero-800.webp 800w, hero-1200.webp 1200w"
  sizes="(max-width: 600px) 400px, (max-width: 1000px) 800px, 1200px"
  src="hero-800.webp"
  alt="Descriptive alt text"
  width="800"
  height="450"
  loading="lazy"
>

3. Font Loading

@font-face {
  font-family: 'BrandFont';
  src: url('brand-font.woff2') format('woff2');
  font-display: swap; /* Always include this */
  font-weight: 400;
}

<!-- Preload critical fonts -->
<link rel="preload" href="brand-font.woff2" as="font" type="font/woff2" crossorigin>

4. Script Loading

<!-- Defer non-critical scripts -->
<script defer src="analytics.js"></script>
<script defer src="interactions.js"></script>

<!-- Async for independent scripts -->
<script async src="third-party-widget.js"></script>

<!-- Never do this -->
<!-- <script src="blocking.js"></script> in <head> -->

5. Preconnect to Third Parties

<head>
  <link rel="preconnect" href="https://fonts.googleapis.com">
  <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
  <link rel="preconnect" href="https://www.googletagmanager.com">
</head>

Performance Budget

Resource	Budget
Total page weight	< 500KB
HTML	< 50KB
CSS	< 50KB
JavaScript	< 100KB
Images (above fold)	< 200KB
Fonts	< 100KB
Third-party scripts	< 50KB

Quick Audit Checklist

Viewport meta tag present
All images have width/height attributes
Below-fold images use loading="lazy"
No render-blocking scripts in <head>
font-display: swap on all @font-face
Critical CSS inlined
Third-party origins preconnected
No unused CSS/JS shipped
Images in WebP/AVIF format
Total page weight under 500KB