Getting up to speed on Core Web Vitals seems to be at the top of everyone's to-do list these days. Just in time for the holidays, we are happy to bring you our new Vitals dashboard to help you get a huge jumpstart.
We love to visualize performance data (in case you haven't heard). We love it even more when we can be true to one of our biggest motivations at SpeedCurve: leveraging both RUM and Synthetic data to help you take action on what matters most.
We’ve been pretty vocal about Core Web Vitals since Google announced this initiative last spring. We love the idea of having a lean, shared set of metrics that we can all rally around – not to mention having a broader conversation about web performance that includes teams throughout an organization.
For many site owners, the increased focus on Core Web Vitals is driven by the fact that Google will be including them as a factor in search ranking in May 2021. Other folks are more interested in distilling the extremely large barrel of performance metrics into an easily digested trinity of guidelines to follow in order to provide a delightful user experience.
We’ve had some time to evaluate and explore these metrics, and we're committed to transparently discussing their pros and cons.
The purpose of this post is to explore First Input Delay (FID). This metric is unique among the three Web Vitals in that it is can only be measured using real user monitoring (RUM), while the other two (Largest Contentful Paint and Cumulative Layout Shift) can be measured using both RUM and synthetic monitoring.
In this post we'll cover:
Let's dig in!
Back in May, we shared that SpeedCurve supports Google's Core Web Vitals in both our synthetic monitoring and LUX real user monitoring tools. Two of the Web Vitals – Largest Contentful Paint (LCP) and First Input Delay (FID) – were actually available in SpeedCurve for quite a while prior to the announcement. The newcomer to the scene was Cumulative Layout Shift (CLS), and, not surprisingly, it's the metric that's gotten the most questions.
A few of the questions I've been asked (or asked myself) about Cumulative Layout Shift:
Six months in, I've had a chance to gather and look at a lot of data, talk with customers, and learn from our friends in the performance community. Here's what I've learned so far.
One of the big challenges with Google's new Cumulative Layout Shift (CLS) metric is understanding which elements actually moved on the page, when they moved, and by how much. To help with debugging your CLS scores, we've added a new visualization to SpeedCurve that shows each layout shift and how each individual shift adds up to the final cumulative metric.
For each layout shift, we show you the filmstrip frame right before and right after the shift. We then draw a red box around the elements that moved, highlighting exactly which elements caused the shift. The Layout Shift Score for each shift also helps you understand the impact of that shift and how it adds to the cumulative score.
Is your site fast? Adding to a string of recent announcements including Lighthouse v6 and Core Web Vitals, Google has introduced Fast page labelling in Chrome 85 for Android. If you are curious about what this means for your site and how you can get in front of it, read on!
Google recently announced an initiative called 'Web Vitals', which focuses on three performance metrics they consider essential for improving the user experience:
With the exception of FID, all of these metrics are available in both LUX (our RUM tool) and Synthetic. FID requires a real user for calculation and therefore is only available in LUX. In place of FID for Synthetic, we recommend tracking JS Long Tasks or Total Blocking Time as an alternative CPU metric.