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Remove dead rules from stylesheets and defer the loading of CSS not used for above-the-fold content to reduce unnecessary bytes consumed by network activity

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)

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

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

Estimated Input Latency is an estimate of how long your app takes to respond to user input, in milliseconds, during the busiest 5s window of page load. If your latency is higher than 50 ms, users may perceive your app as laggy

Preload the image used by the LCP element in order to improve your LCP time

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

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

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 JPEG 2000, JPEG XR, and WebP often provide better compression than PNG or JPEG, which means faster downloads and less data consumption

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

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

This is the largest contentful element painted within the viewport

First CPU Idle marks the first time at which the page's main thread is quiet enough to handle input. [Learn more](https://web.dev/first-cpu-idle/).

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

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

Animations which are not composited can be janky and increase CLS

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

Redirects introduce additional delays before the page can be loaded

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

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

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

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

Descriptive link text helps search engines understand your content

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

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

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

These DOM elements contribute most to the CLS of the page.

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

Some third-party scripts may contain known security vulnerabilities that are easily identified and exploited by attackers

Optimized images load faster and consume less cellular data

Remove unused JavaScript to reduce bytes consumed by network activity

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

Consider using `<link rel=preload>` to prioritize fetching resources that are currently requested later in page load

Descriptive link text helps search engines understand your content

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

Remove dead rules from stylesheets and defer the loading of CSS not used for above-the-fold content to reduce unnecessary bytes consumed by network activity

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 using `<link rel=preload>` to prioritize fetching resources that are currently requested later in page load

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

Preload the image used by the LCP element in order to improve your LCP time

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

These DOM elements contribute most to the CLS of the page.

First Contentful Paint 3G marks the time at which the first text or image is painted while on a 3G network

Optimized images load faster and consume less cellular data

Redirects introduce additional delays before the page can be loaded

Animations which are not composited can be janky and increase CLS

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

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

First CPU Idle marks the first time at which the page's main thread is quiet enough to handle input. [Learn more](https://web.dev/first-cpu-idle/).

Some third-party scripts may contain known security vulnerabilities that are easily identified and exploited by attackers

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

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

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

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

Estimated Input Latency is an estimate of how long your app takes to respond to user input, in milliseconds, during the busiest 5s window of page load. If your latency is higher than 50 ms, users may perceive your app as laggy

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

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

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

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

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

This is the largest contentful element painted within the viewport

Image formats like JPEG 2000, JPEG XR, and WebP often provide better compression than PNG or JPEG, which means faster downloads and less data consumption

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

Remove unused JavaScript to reduce bytes consumed by network activity

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

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

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

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

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