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

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

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

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)

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

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

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

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 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

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

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 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

Minifying JavaScript files can reduce payload sizes and script parse time

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

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

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

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

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

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

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

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

This is the largest contentful element painted within the viewport

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

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

Descriptive link text helps search engines understand your content

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

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

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

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

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

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

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

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

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

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

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/).

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 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)

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

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

This is the largest contentful element painted within the viewport

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

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

Minifying JavaScript files can reduce payload sizes and script parse time

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

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

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

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

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

Descriptive link text helps search engines understand your content

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

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