Preload Scanner

What is the preload scanner?

The preload scanner is a built-in browser optimization that opportunistically parses raw HTML markup parallel to the primary HTML parser, which builds the Document Object Model (DOM).

Why the preload scanner matters for SEO

The preload scanner is important for SEO because it can be leveraged to improve page speed performance and Core Web Vitals.

Preload scanner tips

• Use defer or async attributes for non-render-blocking JavaScript.
• Inline render-blocking CSS.
• Use preload links for assets used in CSS and JavaScript files that are required for rendering the page within the viewport (above the fold).
• Lazy-load images outside the viewport.
• Use Chrome Dev Tools or WebPageTest to discover, optimize, and test render-blocking resources and page performance.

Preload scanner resources

• Chrome Dev Tools
• WebPageTest

Written by Jon Henshaw, published on 04/7/2024, and last updated on 04/10/2024.