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Many APIs, typically reading layout geometry, force the rendering engine to pause script execution in order to calculate the style and layout. Learn more about forced reflow and its mitigations.

A long cache lifetime can speed up repeat visits to your page. Learn more.

A large DOM can increase the duration of style calculations and layout reflows, impacting page responsiveness. A large DOM will also increase memory usage. Learn how to avoid an excessive DOM size.

Your first network request is the most important. Reduce its latency by avoiding redirects, ensuring a fast server response, and enabling text compression.

Requests are blocking the page's initial render, which may delay LCP. Deferring or inlining can move these network requests out of the critical path.

Reducing the download time of images can improve the perceived load time of the page and LCP. Learn more about optimizing image size

Time to Interactive is the amount of time it takes for the page to become fully interactive. Learn more about the Time to Interactive metric.

Redirects introduce additional delays before the page can be loaded. Learn how to avoid page redirects.

Serve images that are appropriately-sized to save cellular data and improve load time. Learn how to size images.

Resources are blocking the first paint of your page. Consider delivering critical JS/CSS inline and deferring all non-critical JS/styles. Learn how to eliminate render-blocking resources.

Reduce unused JavaScript and defer loading scripts until they are required to decrease bytes consumed by network activity. Learn how to reduce unused JavaScript.

Image formats like WebP and AVIF often provide better compression than PNG or JPEG, which means faster downloads and less data consumption. Learn more about modern image formats.

This is the largest contentful element painted within the viewport. Learn more about the Largest Contentful Paint element

Set an explicit width and height on image elements to reduce layout shifts and improve CLS. Learn how to set image dimensions

A large DOM will increase memory usage, cause longer style calculations, and produce costly layout reflows. Learn how to avoid an excessive DOM size.

Text-based resources should be served with compression (gzip, deflate or brotli) to minimize total network bytes. Learn more about text compression.

A long cache lifetime can speed up repeat visits to your page. Learn more about efficient cache policies.

Minifying JavaScript files can reduce payload sizes and script parse time. Learn how to minify JavaScript.

Optimized images load faster and consume less cellular data. Learn how to efficiently encode images.

Large network payloads cost users real money and are highly correlated with long load times. Learn how to reduce payload sizes.

Consider lazy-loading offscreen and hidden images after all critical resources have finished loading to lower time to interactive. Learn how to defer offscreen images.

Informative elements should aim for short, descriptive alternate text. Decorative elements can be ignored with an empty alt attribute. Learn more about the `alt` attribute.

Specifying a doctype prevents the browser from switching to quirks-mode. Learn more about the doctype declaration. Document must contain a doctype

All sites should be protected with HTTPS, even ones that don't handle sensitive data. This includes avoiding mixed content, where some resources are loaded over HTTP despite the initial request being served over HTTPS. HTTPS prevents intruders from tampering with or passively listening in on the communications between your app and your users, and is a prerequisite for HTTP/2 and many new web platform APIs. Learn more about HTTPS.

Make sure that you redirect all HTTP traffic to HTTPS in order to enable secure web features for all your users. Learn more.

Image display dimensions should match natural aspect ratio. Learn more about image aspect ratio.

Image natural dimensions should be proportional to the display size and the pixel ratio to maximize image clarity. Learn how to provide responsive images.

Screen readers have a specific way of announcing lists. Ensuring proper list structure aids screen reader output. Learn more about proper list structure.

When definition lists are not properly marked up, screen readers may produce confusing or inaccurate output. Learn how to structure definition lists correctly.

Informative elements should aim for short, descriptive alternate text. Decorative elements can be ignored with an empty alt attribute. Learn more about the `alt` attribute.

Low-contrast text is difficult or impossible for many users to read. Learn how to provide sufficient color contrast.

Touch targets with sufficient size and spacing help users who may have difficulty targeting small controls to activate the targets. Learn more about touch targets.

If a page doesn't specify a `lang` attribute, a screen reader assumes that the page is in the default language that the user chose when setting up the screen reader. If the page isn't actually in the default language, then the screen reader might not announce the page's text correctly. Learn more about the `lang` attribute.

Properly ordered headings that do not skip levels convey the semantic structure of the page, making it easier to navigate and understand when using assistive technologies. Learn more about heading order.