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

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

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

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

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 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

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

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

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

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

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

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

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

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

This is the largest contentful element painted within the viewport

Remove unused JavaScript to reduce bytes consumed by network activity

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

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

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

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

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

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

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/).

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

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

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

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

Cumulative Layout Shift measures the movement of visible elements 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

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

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

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

This is the largest contentful element painted within the viewport

Remove unused JavaScript to reduce bytes consumed by network activity

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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/).

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)

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

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

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

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

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

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

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