Chrome Developer Summit 2019: Performance Announcements You Have to Know

Profile photo of Karolina Szczur

Karolina Szczur

November 14, 2019

Chrome Developer Summit is a yearly event focusing on new developments in web platform technologies. Over two days, people working directly on Chrome share updates to the ecosystem, tools and approaches to help us in building better, more engaging experiences. Because both Google and even more specifically, Chrome, put a strong emphasis on speed, a lot of announcements are about performance.

If you haven’t had a chance to attend or watch the talks remotely, we’ve hand-picked the most important performance and user experience updates.


Chrome to visually mark slow loading sites

We already know that slow-performing sites are penalized by the search ranking algorithm. Still, Chrome is taking further steps to highlight that a given site might offer a suboptimal user experience. The notices will most likely take a form of new interface elements and warnings built into Chrome.

Possible implementation of Chrome interface highlighting slow websites. Credit: Chromium Blog.

It’s still uncertain how exactly the pages will be evaluated to form a cohesive user experience score, but speed will be one of the defining factors. Now is probably a great time to focus on long-term performance strategies to avoid being marked as slow in the future.

Targetting lower-end devices in React just got easier

Adaptive Loading Hooks is a suite for the React ecosystem, making it easier to target lower-end devices. We can establish specific patterns for resource loading, data-fetching, code-splitting and capability toggling. Effectively, it becomes possible to tailor the experience accordingly to device types, connection speed and user-specific preferences like Data Saver mode.

Credit: Addy Osmani.

Adaptive Loading Hooks can quickly become an indispensable toolkit to ensure users with slower devices and on sluggish networks aren’t disadvantaged in terms of experience.

New metrics: Largest Contentful Paint and Cumulative Layout Shift

Largest Contentful Paint (LCP), Total Blocking Time (TBT) and Cumulative Layout Shift (CLS) represent a new generation of performance metrics, focusing on quantifying user experience beyond the initial load (like First Contentful Paint or First Meaningful Paint do).

Read more about Total Blocking Time.

Not only those metrics showcase what happens after the first paint, but also how stable and responsive interfaces are. Especially with the prevalence of JavaScript and DOM manipulation, metrics focusing on runtime responsiveness and visual stability are becoming crucial to grading excellent performance.

Both LCP and TBT are already available in Calibre—you can track and set budgets against them.

Lighthouse 6 will change how performance score is calculated

Significant changes are coming to Lighthouse 6, due to be released in January. The scoring algorithm will be overhauled to emphasize the importance of new metrics mentioned above. First CPU Idle and First Meaningful Paint will be replaced with Total Blocking Time and Largest Contentful Paint. The weighting of metrics, which we’ve described before when writing about PageSpeed scores, will also change to be more balanced between initial load and interactivity. Cumulative Layout Shift will also eventually make it to Lighthouse scoring algorithm in the future.

Credit: Paul Irish and Elizabeth Sweeny.

What this means to anyone using Lighthouse, whether standalone or in Calibre, is a change in the reported results of their sites. In some cases, the difference might be minor, but quite significant in others. It’s important to know that it doesn’t necessarily mean a performance regression that has happened suddenly, but a more accurate portrayal of real user experience.


All of those announcements show a continuous effort in improving the accuracy of synthetic performance testing. Again, Google is implementing multiple strategies to reward fast sites and penalize slow ones. Reliable performance monitoring solutions are now indispensable in ensuring our products aren’t effectively marked as subpar or degraded in SEO. It has become too costly not to prioritize user experience.

Profile photo of Karolina Szczur

Karolina Szczur

Karolina is the Design Lead at Calibre. With years of design experience under her belt, she’s responsible for the comprehensive user experience spanning over product, visuals and copywriting. Find her on Twitter or LinkedIn.

Related posts

Getting Started with Web Performance

Don’t miss another article

Be notified about new product features, releases and performance research.