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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

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

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

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 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

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

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

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

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

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

This is the largest contentful element painted within the viewport

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

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)

Minifying JavaScript files can reduce payload sizes and script parse time

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

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

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

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

Optimized images load faster and consume less cellular data

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

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

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

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

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/).

Redirects introduce additional delays before the page can be loaded

Descriptive link text helps search engines understand your content

Remove unused JavaScript to reduce bytes consumed by network activity

Animations which are not composited can be janky and increase CLS

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

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

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

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

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

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

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

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

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

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/).

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

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

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

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

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

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

This is the largest contentful element painted within the viewport

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

Optimized images load faster and consume less cellular data

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

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

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

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

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

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

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

Redirects introduce additional delays before the page can be loaded

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

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

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

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

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

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

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

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

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

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

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)

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

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