WebPageTest News: The New CLS, Changelog, & Login System

Windows, windows, everywhere! The Chrome team has changed the way CLS is reported and Tim Kadlec dives deeper into the impact. [WebPageTest Logo] News April 15, 2021 [CLS Windows Email-min] The Google Chrome team is changing the reporting of a key Core Web Vitals metric: [Cumulative Layout Shift (CLS).]( To help long-session pages (SPAs, infinite scrolling, etc.), sessions will be broken into 'windows' of shifts and the max score from each window will be reported as the CLS score. This is a 'shift' (see what we did there?) from the previous method of calculating CLS: summing all shifts. In the latest WPT blog post, Tim Kadlec details the change and tests Ecommerce and news pages to measure the impact. [Read More]( p.s. WebPageTest [now reports]( the windowed version of CLS as the main CLS metric. [WebPageTest Change Log]( has arrived. Stay on top of new metrics and features. New login system, who dis? As you may have noticed, we've consolidated the login experience into a single log in for all of WebPageTest, including: the forums, test history, and [API]( subscription. [Register here]( if you signed up before April 6. In other news: - [Is WebAssembly magic performance pixie dust?]( Article | Surma, April 13 - [How to use WebPageTest's Graph Page Data view]( Article | Matt Hobbs, April 13 - [Who has the fastest F1 website in 2021? Part 8: McClaren Time!]( Article | Jake Archibald, April 14 - [Evolving the CLS Metric]( Article | Annie Sullivan and Hongbo Song, April 7 - [The Chrome team's OKRs for web performance APIs]( Objectives | Chrome Team Catchpoint, 150 West 30th Street, Suite 3, New York, New York 10001, United States [Unsubscribe]( [Manage preferences](