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Website performance guides
Learn what common performance findings mean, why they matter, and what to check before turning them into fix work.
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Use search or categories to jump to problems about LCP, CLS, JavaScript, CSS, images, fonts, and cache.
Common problems
Where teams usually start
The most frequent causes of poor performance that often appear in reports.
Largest Contentful Paint measures when the largest visible content element appears in the viewport. Poor LCP often poi...
Render-blocking resourcesRender-blocking resources are files the browser must process before it can render important content. Not all blocking...
Unused JavaScriptUnused JavaScript increases page weight and main-thread work even when users never use that code. It is common in larg...
Image optimizationImages can strongly affect LCP, bandwidth and mobile loading. The first image to inspect is usually the hero or larges...
All guides
Core performance issue guides
Each card shows the problem type, what it affects, and where to go next.
Largest Contentful Paint
Largest Contentful Paint measures when the largest visible content element appears in the viewport. Poor LCP often points to slow server response, blocking resources, unoptimized hero images...
Cumulative Layout Shift
Cumulative Layout Shift measures unexpected movement of visible content. Poor CLS is often caused by images without dimensions, ads or embeds without reserved space, late-loading fonts, bann...
Total Blocking Time and INP
Total Blocking Time is a lab metric that shows how much long main-thread work blocks the browser during page load. INP is a Core Web Vitals responsiveness metric and is not the same as TBT,...
Render-blocking resources
Render-blocking resources are files the browser must process before it can render important content. Not all blocking CSS is bad, but non-critical CSS and JavaScript should not delay the fir...
Unused JavaScript
Unused JavaScript increases page weight and main-thread work even when users never use that code. It is common in large frameworks, tag managers, WordPress plugins and global bundles. ViewMe...
Unused CSS
Unused CSS is stylesheet code that is delivered to a page but not needed for the current view. It can increase download size and contribute to render-blocking work. ViewMend helps identify t...
Image optimization
Images can strongly affect LCP, bandwidth and mobile loading. The first image to inspect is usually the hero or largest above-the-fold visual, while below-the-fold images should often be laz...
Font loading
Font loading can delay visible text or cause layout shifts when fallback fonts swap to web fonts. Too many weights, external font CSS and missing font-display rules can make the problem wors...
Third-party code
Third-party code can add network requests, JavaScript execution and main-thread blocking. Not all third-party code is bad, but every tag should justify its cost and load at the right time. V...
Efficient cache policy
An efficient cache policy tells browsers how long they can reuse assets. It does not fully fix first-visit performance, but it can reduce repeat load cost for CSS, JavaScript, images and fon...
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