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

Time To First Byte identifies the time at which your server sends a response

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

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

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

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

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

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

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

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

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

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

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

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 long cache lifetime can speed up repeat visits to your page

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

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

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

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

Minifying CSS files can reduce network payload sizes

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

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

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 long cache lifetime can speed up repeat visits to your page

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

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

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

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

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

Minifying CSS files can reduce network payload sizes

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

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

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

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

Time To First Byte identifies the time at which your server sends a response

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

Optimized images load faster and consume less cellular data

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.

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

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

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

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

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

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

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

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

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

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