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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Animations which are not composited can be janky and increase CLS

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

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

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

This is the largest contentful element painted within the viewport

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

Redirects introduce additional delays before the page can be loaded

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

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

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

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

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

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

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

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

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

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

Redirects introduce additional delays before the page can be loaded

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

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

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

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

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

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

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

Animations which are not composited can be janky and increase CLS

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

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

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

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

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

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

This is the largest contentful element painted within the viewport

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

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

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

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)

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

Optimized images load faster and consume less cellular data

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

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

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