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

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

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

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

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

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

Descriptive link text helps search engines understand your content

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 JavaScript libraries can lead to poor performance. Prefer smaller, functionally equivalent libraries to reduce your bundle size

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

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

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

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

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

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

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 long cache lifetime can speed up repeat visits to your page

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

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

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/).

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

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

This is the largest contentful element painted within the viewport

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

Remove unused JavaScript to reduce bytes consumed by network activity

Redirects introduce additional delays before the page can be loaded

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

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

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

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

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

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 servedover 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

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

A fast page load over a cellular network ensures a good mobile user experience

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

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

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 servedover 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

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

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 long cache lifetime can speed up repeat visits to your page

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

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

A fast page load over a cellular network ensures a good mobile user experience

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

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

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

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

Redirects introduce additional delays before the page can be loaded

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

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

Remove unused JavaScript to reduce bytes consumed by network activity

Descriptive link text helps search engines understand your content

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

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 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

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

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

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

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

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

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

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

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

Large JavaScript libraries can lead to poor performance. Prefer smaller, functionally equivalent libraries to reduce your bundle size

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

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

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/).

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