I've just release v6.0.0 of the web-vitals library. It includes support for measuring Web Vitals per soft navigation (like those used in SPAs) for supporting browsers (Chrome 151+) to give more accurate performance metrics for those sites. github.com/GoogleChrome...

I don't know if this article will resonate or not, but I felt it necessary to write. I explore the risks of AI software development, defects, and the challenges of building a mental model when the agent does more and more www.ethangardner.com/posts/ai-age...

The Hidden Quality Risks in AI-Agentic Development

Agentic workflows can hide the cost/quality trade-off rather than remove it, making defects harder to trace back to their source.

ethangardner.com

The first part of Declarative Partial Updates (`<template for>` out-of-order HTML) is now available, unflagged, in Chrome 150!! developer.chrome.com/release-note... The second part (the new JS setting APIs, include the streaming ones) we're still working on the spec side, but maybe for Chrome 152?

Chrome 150  |  Release notes  |  Chrome for Developers

CSS text-fit property, background-clip border-area, Focusgroup, and more.

developer.chrome.com

The Chrome DevTools team are doing a "papercuts" sprint where they try to address lots of small, irritating bugs and annoyances. Reply with crbug.com links (no bug, no fix—that's the deal!) and will see what we can do. No promises though as some may be features/too big/unclear how to solve.

My presentation, Making Performance Allies from @perfnow.nl just got posted to YouTube - www.youtube.com/watch?v=ygdx.... The tips I share in the presentation were designed to make #webperf stick beyond the occasional task that finds its way out of the backlog. Enjoy!

Making Performance Allies - Ethan Gardner - performance.now() 2025

YouTube video by Web Conferences Amsterdam

youtube.com

Our favourite conference of the year is back: CSS Day ✨ CSS legends, browser engineers, and web platform experts sharing talks on modern CSS, accessibility, design systems, browser internals, and much more. cssday.nl See you next week in Amsterdam? ☕️

CSS Day 2026, 11th & 12th of June, Amsterdam

CSS Day is the conference for CSS designers, developers, spec writers, and browser vendors.

cssday.nl

I did a 10-minute DevTools audit of a top 10k site with real RUM tooling installed. Every Core Web Vitals metric: poor. The hero image isn't preloaded. The tag manager, consent tool, and coupon service are. Organizational influence showed up in the preloads. www.ethangardner.com/posts/lightn...

What 10 Minutes Revealed About Web Performance and Organizational Priorities

A 10-minute DevTools audit of a top 10k website reveals heavy pages, poor Core Web Vitals, and a preload list that reads like competing team priorities

ethangardner.com

I'm really excited for this one, especially for design systems where it will shed more light on component performance.

Barry Pollard@tunetheweb.com · 3mo ago

There's a new #webperf measurement API in the works! Check out this post looking at the work @jason-williams.co.uk and @jdapena.bsky.social have been putting into there Container Timing—available as an origin trail from Chrome 148 (rolling out next week). developer.chrome.com/blog/contain...

In response to our objection to the Prompt API, some folks replied "well, fix it. Propose something better". This is something we end up doing a lot at Firefox…

It's almost time to implement the Soft Navigations API to accurately measure Core Web Vitals for SPAs (React, Vue, Angular, etc.). We applied your feedback to build the expected final shape. Conduct a final test during the origin trial in Chrome 147-149 → goo.gle/4ttf9eP

Layout shifts often only happen at specific screen sizes or after a user interaction. That's why I built a new free tool: the CLS checker tests your site at 5 different viewport sizes and scrolls down the page. Try it out here: www.debugbear.com/test/cls

I'm very excited about this! Have seen some really significant impact in our tests. With the sizes of websites and JS payloads continuing to increase, this is both important and impactful.

Cloudflare@cloudflare.social · 4mo ago

Today, we’re excited to give you a sneak peek of our support for shared compression dictionaries, show you how it improves page load times, and reveal when you’ll be able to try the beta yourself. https://cfl.re/42egXfC

I recently analyzed data from the HTTP Archive to see how the web has changed since the launch and adoption of AI tools. The results show a clear trend. The web is getting heavier at an accelerated rate. www.ethangardner.com/posts/object...

An Objective Analysis of AI's Impact on Page Weight

What has happened with page weight with the adoption of AI?

ethangardner.com

Performance isn’t just about the first click; it’s about the entire journey. By making sure your pages are eligible for bfcache, you remove the technical hurdles of the network and CPU, creating a browsing experience that feels as fast as a native app. www.ethangardner.com/posts/bfcach...

Back/Forward Cache Demo and Debugging

Using bfcache to plug holes in your site's conversion funnel.

ethangardner.com

I'm listening to an audio book and the author said that he encountered software with more bugs than the Amazon, and I am totally stealing that expression.

🎨 I gotta say, my latest is a little treasure trove: what even is `contain`?! csswizardry.com/2026/04/what...

⚡WebPerformance Report is more than a report in your inbox. Users also get access to their Board to manage reports, review deliveries, and follow Performance, Accessibility, and Security trends over time. Get your report here: 👉https://webperformancereport.com/ #webperf

p75 and p90 JavaScript bytes on the web have exploded since May, 2025—easily the largest 10 month period based on HTTP Archive data since 2023. The long-tail is getting worse, very quickly. Gemini, what happened in May 2025?

⚡Featured posts this week: ✨ Telescope Test Agent: Mike Kozicki @nywebperf.com ✨ Agentic SEO for e-commerce: Emilie Wilhelm ✨ The Hidden Costs Behind Modern Frontend: Juntao Qiu ✨ Web Performance Archetypes: @ethangardner.com rdner 🙏 Special thanks to the authors! #webperf

✨ Core Web Vitals Summit: The Videos ✨ I'll be sharing the recorded sessions from the Summit stream, and some brief commentary on some takeaways and significance. All are welcome to join the conversation! 📆 Monday March 23rd ⏰ 1pm EST, 10am PST 🔗 www.youtube.com/live/LXYcknO...

Is it really possible to anticipate shifts in RUM data from immediate LAB results, using machine learning (ML)? We're going to find out with @ethangardner.com. Joins us for that conversation ✨ SPDY STREAM 027 ✨ 📆 Tomorrow, Wednesday March 18th ⏰ 1pm EST, 10am PST 🔗 www.youtube.com/live/ZEy0lRq...

Your website has a UX Score and you've probably never seen it. It's based on real Chrome user data from real visits. Not a lab test. Not a guess. Enter any URL, get your score in 10 seconds: www.iron-out.io/benchmark Free. No login 🚀

Free UX Score Check — Website Performance Benchmark

Check your UX Score for free. Real CrUX data across LCP, INP, CLS, TTFB and FCP. Benchmark against the top 300 Dutch websites. No login required.

iron-out.io

Yes, I know it's Friday… but I deployed this anyway! 😎 We added the No-Vary-Search response header to a bunch of sites to ignore tracking parameters like `utm_*`, `gclid`, and `fbclid`. They’re consumed by third party tracking scripts, but they should not create .. 1/4

A slow UX affects people’s perception of three important brand elements that are completely unrelated to page speed: content, design, and usability. Here's why that takeaway is relevant in an increasingly competition online landscape 👉 www.speedcurve.com/blog/brand-p... #webperf #ux #pagespeed

SpeedCurve | The speed of trust: How slow pages hurt your brand

In a competitive market, page speed is as important as your design and content.

speedcurve.com

Web performance metrics aren’t just engineering diagnostics. They’re large-scale UX research. They reveal friction, bias, and experience gaps usability studies alone can’t see. I wrote about this intersection: www.ethangardner.com/posts/web-pe... #ux #webperf

Performance is UX: What Web Performance Optimization Can Do for UX Researchers

Understand how web performance metrics connect to UX research outcomes.

ethangardner.com

How I use Web Components with ShadowDOM in a Design System. www.ethangardner.com/posts/shadow...

How I Use ShadowDOM with Web Components in Design Systems

Web components and CSS custom properties can create a future-proof design system with maximum flexibility

ethangardner.com

Back to work tomorrow. This is my reflection on 2025. www.ethangardner.com/posts/2025-y...

Web performance calendar day 3 when @ethangardner.com shows us how to train a ML model on synthetic perf metrics and use it to predict approximate field data before a page/feature goes live. calendar.perfplanet.com/2025/traffic...

Traffic Modeling Using Machine Learning

When I explain the difference between lab (aka synthetic) and field data to people, one of the things I mention is that the lab allows for testing under repeatable, controlled conditions. Each test ru...

calendar.perfplanet.com

How's the mobile CPU landscape evolving? Thanks to process node improvements, a mid-range Android from 2025 is (finally!) as fast as 2017's iPhone 8, but a low-end (~$100) smartphone isn't yet as speedy as a decade-old iPhone 6s.

My talk at Performance.sync() pre-conference meetup organized by @mozilla.org in Amsterdam last week: www.youtube.com/watch?v=2cv6...

7 Levels of a Web Performance Journey - Sergey Chernyshev - performance.sync() 2025

YouTube video by Web Conferences Amsterdam

youtube.com