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

Optimized images load faster and consume less cellular data

First Contentful Paint marks the time at which the first 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)

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

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

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

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

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

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

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

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

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

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

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

These DOM elements were most affected by layout shifts. Some layout shifts may not be included in the CLS metric value due to [windowing](https://web.dev/articles/cls#what_is_cls)

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

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

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

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

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

Service worker is the technology that enables your app to use many Progressive Web App features, such as offline, add to homescreen, and push notifications. With proper service worker and manifest implementations, browsers can proactively prompt users to add your app to their homescreen, which can lead to higher engagement

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

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