Speed Index shows how quickly the contents of a page are visibly populated

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

Polyfills and transforms enable legacy browsers to use new JavaScript features. However, many aren't necessary for modern browsers. For your bundled JavaScript, adopt a modern script deployment strategy using module/nomodule feature detection to reduce the amount of code shipped to modern browsers, while retaining support for legacy browsers

Resources are blocking the first paint of your page. Consider delivering critical JS/CSS inline and deferring all non-critical JS/styles

First Meaningful Paint measures when the primary content of a page is visible

The maximum potential First Input Delay that your users could experience is the duration of the longest task

Consider instrumenting your app with the User Timing API to measure your app's real-world performance during key user experiences

Cumulative Layout Shift measures the movement of visible elements within the viewport

Deprecated APIs will eventually be removed from the browser

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

Animations which are not composited can be janky and increase CLS

Keep the server response time for the main document short because all other requests depend on it

Consider reducing the time spent parsing, compiling, and executing JS. You may find delivering smaller JS payloads helps with this

Image formats like WebP and AVIF often provide better compression than PNG or JPEG, which means faster downloads and less data consumption

Sum of all time periods between FCP and Time to Interactive, when task length exceeded 50ms, expressed in milliseconds

Minifying JavaScript files can reduce payload sizes and script parse time

Lists the longest tasks on the main thread, useful for identifying worst contributors to input delay

First Contentful Paint marks the time at which the first text or image is painted

Large network payloads cost users real money and are highly correlated with long load times

This is the largest contentful element painted within the viewport

Largest Contentful Paint marks the time at which the largest text or image is painted

Minifying CSS files can reduce network payload sizes

Reduce unused rules from stylesheets and defer CSS not used for above-the-fold content to decrease bytes consumed by network activity

Third-party code can significantly impact load performance. Limit the number of redundant third-party providers and try to load third-party code after your page has primarily finished loading

These are the largest layout shifts observed on the page. Each table item represents a single layout shift, and shows the element that shifted the most. Below each item are possible root causes that led to the layout shift. Some of these layout shifts may not be included in the CLS metric value due to [windowing](https://web.dev/articles/cls#what_is_cls)

A large DOM will increase memory usage, cause longer [style calculations](https://developers.google.com/web/fundamentals/performance/rendering/reduce-the-scope-and-complexity-of-style-calculations), and produce costly [layout reflows](https://developers.google.com/speed/articles/reflow)

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

The Critical Request Chains below show you what resources are loaded with a high priority. Consider reducing the length of chains, reducing the download size of resources, or deferring the download of unnecessary resources to improve page load

Optimized images load faster and consume less cellular data

Network round trip times (RTT) have a large impact on performance. If the RTT to an origin is high, it's an indication that servers closer to the user could improve performance

Time to Interactive is the amount of time it takes for the page to become fully interactive

Consider reducing the time spent parsing, compiling and executing JS. You may find delivering smaller JS payloads helps with this

Serve images that are appropriately-sized to save cellular data and improve load time

Server latencies can impact web performance. If the server latency of an origin is high, it's an indication the server is overloaded or has poor backend performance

First Meaningful Paint measures when the primary content of a page is visible

Network round trip times (RTT) have a large impact on performance. If the RTT to an origin is high, it's an indication that servers closer to the user could improve performance

The Critical Request Chains below show you what resources are loaded with a high priority. Consider reducing the length of chains, reducing the download size of resources, or deferring the download of unnecessary resources to improve page load

Resources are blocking the first paint of your page. Consider delivering critical JS/CSS inline and deferring all non-critical JS/styles

Lists the longest tasks on the main thread, useful for identifying worst contributors to input delay

These are the largest layout shifts observed on the page. Each table item represents a single layout shift, and shows the element that shifted the most. Below each item are possible root causes that led to the layout shift. Some of these layout shifts may not be included in the CLS metric value due to [windowing](https://web.dev/articles/cls#what_is_cls)

Deprecated APIs will eventually be removed from the browser

Serve images that are appropriately-sized to save cellular data and improve load time

Font sizes less than 12px are too small to be legible and require mobile visitors to “pinch to zoom” in order to read. Strive to have >60% of page text ≥12px

The maximum potential First Input Delay that your users could experience is the duration of the longest task

Keep the server response time for the main document short because all other requests depend on it

Large network payloads cost users real money and are highly correlated with long load times

Image formats like WebP and AVIF often provide better compression than PNG or JPEG, which means faster downloads and less data consumption

This is the largest contentful element painted within the viewport

Sum of all time periods between FCP and Time to Interactive, when task length exceeded 50ms, expressed in milliseconds

Speed Index shows how quickly the contents of a page are visibly populated

Server latencies can impact web performance. If the server latency of an origin is high, it's an indication the server is overloaded or has poor backend performance

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

Minifying JavaScript files can reduce payload sizes and script parse time

Consider instrumenting your app with the User Timing API to measure your app's real-world performance during key user experiences

Third-party code can significantly impact load performance. Limit the number of redundant third-party providers and try to load third-party code after your page has primarily finished loading

Cumulative Layout Shift measures the movement of visible elements within the viewport

Optimized images load faster and consume less cellular data

Time to Interactive is the amount of time it takes for the page to become fully interactive

Consider reducing the time spent parsing, compiling and executing JS. You may find delivering smaller JS payloads helps with this

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

Polyfills and transforms enable legacy browsers to use new JavaScript features. However, many aren't necessary for modern browsers. For your bundled JavaScript, adopt a modern script deployment strategy using module/nomodule feature detection to reduce the amount of code shipped to modern browsers, while retaining support for legacy browsers

Consider reducing the time spent parsing, compiling, and executing JS. You may find delivering smaller JS payloads helps with this

A large DOM will increase memory usage, cause longer [style calculations](https://developers.google.com/web/fundamentals/performance/rendering/reduce-the-scope-and-complexity-of-style-calculations), and produce costly [layout reflows](https://developers.google.com/speed/articles/reflow)

First Contentful Paint marks the time at which the first text or image is painted

Largest Contentful Paint marks the time at which the largest text or image is painted

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

Minifying CSS files can reduce network payload sizes