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

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)

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

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

All sites should be protected with HTTPS, even ones that don't handle sensitive data. This includes avoiding [mixed content](https://developers.google.com/web/fundamentals/security/prevent-mixed-content/what-is-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

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

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

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

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

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

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

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

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

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

This is the largest contentful element painted within the viewport

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

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

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

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

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

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

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

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

Redirects introduce additional delays before the page can be loaded

Optimized images load faster and consume less cellular data

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 long cache lifetime can speed up repeat visits to your page

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

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

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

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

This is the largest contentful element painted within the viewport

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

All sites should be protected with HTTPS, even ones that don't handle sensitive data. This includes avoiding [mixed content](https://developers.google.com/web/fundamentals/security/prevent-mixed-content/what-is-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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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)

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

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

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

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

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

Redirects introduce additional delays before the page can be loaded

Optimized images load faster and consume less cellular data

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

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

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

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

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