TTFB is the time when the visitor starting to navigate to a page (for example, clicking on a link), until the first bytes of the HTML document are received.
Those looking to optimize LCP should also use the First Contentful Paint (FCP) and Time to First Byte (TTFB) timings, which are good diagnostic metrics that can provide valuable insights into LCP. Using PageSpeed Insights CrUX supplementary metrics # Similarly, it can show which device types have LCP issues. Looking at the four different categories of CrUX data can help you understand whether an LCP issue is specific to this page, or a more general site-wide issue. Home pages tend to be visted by new users and so may often be loaded "cold", without any cached content and so are often the slowest pages on a website. It can also be affected by how visitors navigate to these pages. The LCP for the whole origin may be very different to an individual page's LCP depending on how the LCP is loaded on that page compared to other pages on that origin. Be aware that where a URL does not have sufficient data to be shown at the URL level-but does have data for the origin-PageSpeed Insights will automatically show this. These can be toggled in the controls at the top, and top right-hand side of this section. PageSpeed Insights shows up to four different CrUX data:
#HIDDEN DEEP DEVELOPER HOW TO#
Later in this guide we will explain how to collect this data using JavaScript. This can also provide much more data than CrUX can expose as a public dataset. Where CrUX does not provide data (for example, a page with insufficient traffic to get page-level data), CrUX should be supplemented with RUM data collected using JavaScript APIs running on the web page. If CrUX data is available for your website, always concentrate on the real user data first. More detailed lab-based data is available in the bottom section labeled Diagnose performance issues. PageSpeed Insights provides access to CrUX data in the top section labeled Discover what your real users are experiencing. LCP data based on real users can be surfaced from Real User Monitoring (RUM) tools installed on a site, or via the Chrome User Experience Report (CrUX) which collect anonymous data from real Chrome users for millions of websites. These lab-based tools can give a wealth of information to explain and help you improve LCP, but be aware that lab tests alone may not be entirely representative of what your actual users experience. To understand LCP of real users, we should look at what real users are experiencing, rather than what a lab-based tool like Lighthouse or local testing shows. LCP can be measured in a number of tools and not all of these measure LCP in the same way. Understanding your LCP metric #īefore optimizing LCP, developers should seek to understand if they even have an LCP issue, and the extent of any such issue. To improve LCP you have to look at the entire loading process and make sure every step along the way is optimized.
It's rare that a quick fix to a single part of a page will result in a meaningful improvement to LCP. There are a number of factors that can affect how quickly the browser is able to load and render a web page, and delays across any of them can have a significant impact on LCP. To provide a good user experience, sites should strive to have an LCP of 2.5 seconds or less for at least 75% of page visits. Specifically, LCP measures the time from when the user initiates loading the page until the largest image or text block is rendered within the viewport. Largest Contentful Paint (LCP) is one of the three Core Web Vitals metrics, and it represents how quickly the main content of a web page is loaded.
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