diff --git a/docs/scoring.md b/docs/scoring.md index eb1a52eea734..5942fbf9ebed 100644 --- a/docs/scoring.md +++ b/docs/scoring.md @@ -13,12 +13,13 @@ Note 2: receiving a **score of ?** in any Lighthouse category indicates an error ### What performance metrics does Lighthouse measure? Lighthouse measures the following performance metrics: -- [First meaningful paint](https://developers.google.com/web/tools/lighthouse/audits/first-meaningful-paint): first meaningful paint is defined as when the browser first puts any “meaningful” element/set of “meaningful” elements on the screen. What is meaningful is determined from a series of heuristics. -- [First interactive](https://developers.google.com/web/tools/lighthouse/audits/first-interactive): first interactive is defined as the first point at which the page could respond quickly to input. It doesn't consider any point in time before first meaningful paint. The way this is implemented is primarily based on heuristics. +- [First Contentful Paint](https://developers.google.com/web/fundamentals/performance/user-centric-performance-metrics#first_paint_and_first_contentful_paint): first contentful paint is the first time the browser paints any content (text, image, canvas, etc) on the screen. +- [First Meaningful Paint](https://developers.google.com/web/tools/lighthouse/audits/first-meaningful-paint): first meaningful paint is defined as when the browser first puts any “meaningful” element/set of “meaningful” elements on the screen. What is meaningful is determined from a series of heuristics. +- [First CPU Idle](https://developers.google.com/web/tools/lighthouse/audits/first-interactive): first CPU idle is defined as the first point at which the page could respond quickly to input. It doesn't consider any point in time before first meaningful paint. The way this is implemented is primarily based on heuristics. *Note: this metric is currently in beta, which means that the underlying definition of this metric is in progress.* -- [Consistently interactive](https://developers.google.com/web/tools/lighthouse/audits/consistently-interactive): defined as the first point at which everything is loaded such that the page will quickly respond to any user input throughout the page. +- [Time to Interactive](https://developers.google.com/web/tools/lighthouse/audits/consistently-interactive): defined as the first point at which everything is loaded such that the page will quickly respond to any user input throughout the page. *Note: this metric is currently in beta, which means that the underlying definition of this metric is in progress.* -- [Perceptual Speed Index (pSI)](https://developers.google.com/web/tools/lighthouse/audits/speed-index): pSI measures how many pixels are painted at each given time interval on the viewport. The earlier the pixels are painted, the better you score on metric since we want an experience where most of the content is shown on the screen during the first few moments of initiating the page load. Loading more content earlier makes your end user feel like the website is loading quickly, which contributes to a positive user experience. Therefore, the lower the pSI score, the better. +- [Speed Index](https://developers.google.com/web/tools/lighthouse/audits/speed-index): Speed Index measures how quickly all above-the-fold content is painted on screen. The earlier the pixels are painted, the better you score on metric. Users want an experience where most of the content is shown on the screen during the first few moments of initiating the page load. Loading more content earlier makes your end user feel like the website is loading quickly, which contributes to a positive user experience. Therefore, the lower your Speed Index, the better. - [Estimated Input Latency](https://developers.google.com/web/tools/lighthouse/audits/estimated-input-latency): this audit measures how fast your app is in responding to user input. Our benchmark is that the estimated input latency should be under 50 ms (see documentation [here](https://developers.google.com/web/tools/lighthouse/audits/estimated-input-latency) as to why). *Some **variability** when running on real-world sites is to be expected as sites load different ads, scripts, and network conditions vary for each visit. Note that Lighthouse can especially experience inconsistent behaviors when it runs in the presence of anti-virus scanners, other extensions or programs that interfere with page load, and inconsistent ad behavior. Please try to run without anti-virus scanners or other extensions/programs to get the cleanest results, or alternatively, run Lighthouse on WebPageTest for the most consistent results [here](https://www.webpagetest.org/easy.php).* @@ -42,7 +43,7 @@ These weights are heuristics, and the Lighthouse team is working on formalizing ### How do performance metrics get scored? Once Lighthouse is done gathering the raw performance metrics for your website (metrics reported in miliseconds), it converts them into a score by mapping the raw performance number to a number between 0-100 by looking where your raw performance metric falls on the Lighthouse scoring distribution. The Lighthouse scoring distribution is a log normal distribution that is derived from the performance metrics of real website performance data (see sample distribution [here](https://www.desmos.com/calculator/zrjq6v1ihi)). -Once we finish computing the percentile equivalent of your raw performance score, we take the weighted average of all the performance metrics (per the weighting above, with 5x weight given to first meaningful weight, first interactive, and consistently interactive). Finally, we apply a coloring to the score (green, orange, and red) depending on what "bucket" your score falls in. Roughly, this maps to: +Once we finish computing the percentile equivalent of your raw performance score, we take the weighted average of all the performance metrics (per the weighting above). Finally, we apply a coloring to the score (green, orange, and red) depending on what "bucket" your score falls in. This maps to: - Red (poor score): 0-44. - Orange (average): 45-74 - Green (good): 75-100.