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Performance Module

Module ID: performance | Type: Core (always enabled) | Weight: 15%

The Performance module analyses HTML for page weight, render-blocking resources, lazy loading, image optimisation hints, inline asset sizes, and resource hints.

What It Checks

Check What It Looks For
HTML document size Raw HTML size in bytes
Render-blocking scripts <script> tags without async or defer in <head>
Render-blocking CSS External stylesheets without media attributes
Lazy loading loading="lazy" on below-fold images
Image format Modern formats (WebP, AVIF) vs legacy (PNG, JPEG, GIF)
Inline CSS size Total bytes of <style> blocks
Inline JS size Total bytes of inline <script> blocks
Resource hints preconnect, prefetch, preload link tags
Font loading font-display: swap or equivalent strategy
Third-party scripts Count and size of external domain scripts

Scoring Breakdown

Criterion Deduction Condition
HTML over 100KB -5 Document size exceeds 100KB
HTML over 250KB -10 Document size exceeds 250KB
Render-blocking scripts -5 per script Up to -15 total
Render-blocking CSS -3 per stylesheet Up to -9 total
No lazy loading on images -5 No images use loading="lazy"
No modern image formats -5 All images use legacy formats
Large inline CSS (>50KB) -5 Inline styles exceed 50KB
Large inline JS (>50KB) -5 Inline scripts exceed 50KB
No resource hints -5 No preconnect/prefetch/preload
No font-display strategy -3 Font loading blocks render
Excessive third-party scripts -5 More than 10 external scripts

Auto-Detection

This module is always enabled. Performance affects every site.

Example Findings

P1 HIGH: 4 render-blocking scripts in <head>
  Scripts without async or defer block HTML parsing. The browser cannot
  render anything until these scripts download and execute.
  Fix: Add defer to non-critical scripts, or move them to the end of <body>.
  Effort: Low

P2 MEDIUM: No lazy loading on 12 images
  All images load immediately, increasing initial page weight and time
  to interactive.
  Fix: Add loading="lazy" to images below the fold. Keep above-fold
       images eager-loaded.
  Effort: Low

P3 LOW: No resource hints found
  Resource hints (preconnect, prefetch) help the browser start
  loading critical resources earlier.
  Fix: Add <link rel="preconnect" href="https://fonts.googleapis.com">
       for key third-party origins.
  Effort: Low