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Keep request counts low and transfer sizes small

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Lighthouse reports how many network requests were made and how much data was transferred while your page loaded:

A screenshot of the Lighthouse Keep request counts low and transfer sizes small audit
  • The Requests and Transfer Size values for the Total row are computed by adding the values for the Image, Script, Font, Stylesheet, Other, Document, and Media rows.
  • The Third-party column does not factor into the Total row's values. Its purpose is to make you aware of how many of the total requests and how much of the total transfer size came from third-party domains. The third-party requests could be a combination of any of the other resource types.

Like all of the Diagnostics audits, the Keep request counts low and transfer sizes small audit does not directly affect your Performance score. However, reducing request counts or transfer sizes may improve other Performance metrics.

How to reduce resource counts and transfer sizes

The effect of high resource counts or large transfer sizes on load performance depends on what type of resource is being requested.

CSS and JavaScript

Requests for CSS and JavaScript files are render-blocking by default. In other words, browsers can't render content to the screen until all CSS and JavaScript requests are finished. If any of these files are hosted on a slow server, that single slow server can delay the entire rendering process. See Optimize your JavaScript, Optimize your third-party resources, and Optimize your CSS to learn how to only ship the code that you actually need.

Affected metrics: All

Images

Requests for images aren't render-blocking like CSS and JavaScript, but they can still negatively affect load performance. A common problem is when a mobile user loads a page and sees that images have started loading but will take a while to finish. See Optimize your images to learn how to load images faster.

Affected metrics: First Contentful Paint, First Meaningful Paint, Speed Index

Fonts

Inefficient loading of font files can cause invisible text during the page load. See Optimize your fonts to learn how to default to a font that's available on the user's device and then switch to your custom font when it has finished downloading.

Affected metrics: First Contentful Paint

Documents

If your HTML file is large, the browser has to spend more time parsing the HTML and constructing the DOM tree from the parsed HTML.

Affected metrics: First Contentful Paint

Media

Animated GIF files are often very large. See Replace GIFs with videos to learn how to load animations faster.

Affected metrics: First Contentful Paint

Use performance budgets to prevent regressions

Once you've optimized your code to reduce request counts and transfer sizes, see Set performance budgets to learn how to prevent regressions.

Resources

Source code for Keep request counts low and transfer sizes small audit

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