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

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

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

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

Optimized images load faster and consume less cellular data

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Minifying CSS files can reduce network payload sizes

Text-based resources should be served with compression (gzip, deflate or brotli) to minimize total network bytes

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/).

Minifying JavaScript files can reduce payload sizes and script parse time

This is the largest contentful element painted within the viewport

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

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

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/).

Minifying JavaScript files can reduce payload sizes and script parse time

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

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

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

Remove unused JavaScript to reduce bytes consumed by network activity

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

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

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

Text-based resources should be served with compression (gzip, deflate or brotli) to minimize total network bytes

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Optimized images load faster and consume less cellular data

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

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

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

Minifying CSS files can reduce network payload sizes

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

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