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Interaction to Next Paint, revisiting the Performance Golden Rule & the latest retail page speed benchmarks

Apr 18, 2023


Hi there,

Another month, another selection of the best web performance articles and resources I've come across in my online travels. In this edition:

  • How fast are the top retail sites?
  • Introducing Interaction to Next Paint in SpeedCurve RUM!
  • Revisiting the Performance Golden Rule
  • In our collective pursuit of increasingly complex frameworks, have we sacrificed performance and utility?
  • Web performance resources for front-end developers

Until next month, I hope you stay safe, happy and well. :)

m: @tammy
t: @tameverts


How fast are top retail sites?

For retail sites, slow pages are usually a "death by a thousand cuts" scenario. There's rarely a single big issue. It's typically a myriad of issues – slow backend times, blocking scripts and stylesheets, bloated pages, poorly performing custom fonts, and unoptimized images.

Visiting your site on a newer device over a fast connection can hide those issues. Mobile devices and slow connections expose them.

A recent snapshot of the Page Speed Benchmarks for EU and UK retail sites – tested over a slow mobile connection – shows Largest Contentful Paint (LCP) times as slow as 101 seconds. Google's recommended threshold for LCP is 2.5 seconds.

US retail sites fared a bit better (though still not great) with the slowest LCP time clocking in at 34 seconds.

Page Speed Benchmarks is a public-facing, interactive set of dashboards. We test and rank industry-leading websites based on how fast their pages appear to load from a user’s perspective. It's a handy tool for benchmarking your own site, as well as digging down to see how the fastest and slowest pages in the dashboards are built.


NEW: Interaction to Next Paint and more!

We recently released some exciting product updates:

Interaction to Next Paint – INP is an emerging RUM metric that is poised to replace First Input Delay as the interactivity metric in Core Web Vitals. You can now add INP to your Core Web Vitals dashboard, as well as create performance budgets for it.

Update to Lighthouse 10 – Lighthouse scoring has been updated for the first time since version 8. Metrics and scoring weights include the deprecation of Time to Interactive (TTI) and the increase in weight for Cumulative Layout Shift (CLS).

Cumulative Layout Shift update – We've updated our RUM library to include the latest CLS implementation, which includes session windows. This may have a positive impact on CLS scores, especially for longer lived pages. We've updated this for synthetic, too.


The Performance Golden Rule Revisited

For years and years, one of performance's golden rules has been that 80-90% of end-user response time is spent at the front end. This is why most of our tools and efforts focus on front-end optimization.

Like all rules, it's great to take a fresh look, so Tim Kadlec looked at HTTP Archive data to see if the golden rule holds true. I won't give away his findings, so you'll need to check them out for yourself. ;)


The Market for Lemons

Anything by Alex Russell is always worth a read, and this post is no exception. Alex argues compellingly that complexity merchants have pitched their frameworks hard over the past several years, sacrificing performance and product success along the way:

"...after more than a decade of JS hot air, the framework-centric pitch is still phrased in speculative terms because there's no there there. The complexity merchants can't cop to the fact that management competence and lower complexity — not baroque technology — are determinative of product and end-user success."


Web Performance Resources
for Front End Developers

If you're just getting started in performance – or if you know someone who is – Ben Robertson has compiled a great collection of resources, from articles and courses to tools and books, to kickstart your learning.


ICYMI: Why you need to know your site's performance plateau (and how to find it)

"I made my pages faster, but my business and user engagement metrics didn't change. WHY???"
"How do I know how fast my pages should be?"
"How can I demonstrate the business value of performance to people in my organization?"

If you've ever asked yourself these questions, then you could find the answers in understanding the performance plateau for your site.

The performance plateau is the point at which changes to your website’s rendering metrics (such as Start Render and Largest Contentful Paint) cease to matter because you’ve bottomed out in terms of business and user engagement metrics. In other words, if your performance metrics are on the performance plateau, making them a couple of seconds faster probably won't help your business.


Find us in person at these events!

We're so excited to be sponsors for these upcoming events. If you're planning to attend, let us know. We'd love to see you there!


Questions? Feedback? Let me know!

As always, I welcome your questions and feedback. Let me know your thoughts by replying to this email or sending a note to