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

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

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

These DOM elements contribute most to the CLS of the page

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

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

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

Animations which are not composited can be janky and increase CLS

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

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

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)

Optimized images load faster and consume less cellular data

Remove large, duplicate JavaScript modules from bundles to reduce unnecessary bytes consumed by network activity.

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

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

This is the largest contentful element painted within the viewport

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

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

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

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

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

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

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

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

Large GIFs are inefficient for delivering animated content. Consider using MPEG4/WebM videos for animations and PNG/WebP for static images instead of GIF to save network bytes

To set budgets for the quantity and size of page resources, add a budget.json file

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

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

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

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

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

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

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

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

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

This is the largest contentful element painted within the viewport

Remove large, duplicate JavaScript modules from bundles to reduce unnecessary bytes consumed by network activity.

Animations which are not composited can be janky and increase CLS

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

Optimized images load faster and consume less cellular data

To set budgets for the quantity and size of page resources, add a budget.json file

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

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

Reduce unused rules from stylesheets and defer CSS not used for above-the-fold content 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

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)

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

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

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

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

Interactive elements like buttons and links should be large enough (48x48px), or have enough space around them, to be easy enough to tap without overlapping onto other elements

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

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

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