What is Critical Rendering Path?

The Critical Rendering Path (CRP) is the sequence of steps browsers take to convert HTML, CSS, and JavaScript into pixels on the screen. Understanding and optimizing the CRP is essential for fast page loads in Frontend Accelerator applications.

CRP Steps:

1. DOM Construction: Parse HTML to build the Document Object Model
2. CSSOM Construction: Parse CSS to build the CSS Object Model
3. Render Tree: Combine DOM and CSSOM to create the render tree
4. Layout: Calculate the size and position of each visible element
5. Paint: Convert the render tree into actual pixels on screen

Optimizing CRP in Frontend Accelerator:

• Minimize critical resources using code splitting and dynamic imports
• Defer non-critical JavaScript with Next.js Script component
• Inline critical CSS for above-the-fold content
• Use font-display: swap for web fonts to prevent text blocking
• Leverage Next.js automatic static optimization

Example optimization:

import Script from 'next/script';

<Script src="/analytics.js" strategy="lazyOnload" />

Key Metrics:

• First Contentful Paint (FCP): When first content appears
• Largest Contentful Paint (LCP): When main content is visible
• Time to Interactive (TTI): When page becomes fully interactive

AI-Friendly: The Critical Rendering Path provides a clear mental model of how pages load. AI tools can analyze your application's CRP, identify blocking resources, and suggest specific optimizations like resource hints, preloading critical assets, or adjusting script loading strategies to improve load performance.