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

WebPerformance Report Board displayed on desktop and mobile, showing a Reporting-as-a-Service platform where users can manage reports, review deliveries, and monitor Performance, Accessibility, and Security trends.

⚡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

I talked to @henrihelvetica.bsky.social this week about finding hotspots in codebases using techniques from a book called Your Code as a Crimescene. I think perf budgets and extra guardrails are going to be vital to UX in the future.

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 from Perf Links by WebPerformance Report:

⚡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

SPDY stream Presents: core-web-vital Summit, the videos.

✨ 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...

99.38% uptime. Do I get to pick which 54 hours a year the site is down?

SPDY stream, performance people project projects. Wednesday, March 18, 1 PM Eastern standard time online. Avatar of two persons in black-and-white. Colourful rally car that reads Repsol in branding.

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...

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.

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 🚀

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

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.

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

Performance is UX: What Web Performance Optimization Can Do for UX Researchers Understand how web performance metrics connect to UX research outcomes.

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

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

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

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

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...

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...

Geekbench 6 single-core scores over time at 4 price points: - fastest iOS - fastest Android - mid-tier Android - low-end Android

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.

That would be poor <form>

The nerves are real.

You did great! If you were nervous, I couldn't tell.

7 Levels of a Web Performance Journey - Sergey Chernyshev - performance.sync() 2025 YouTube video by Web Conferences Amsterdam

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

I also made it without any extravagant hand gestures 😜.

Web Performance Allies - PerfNow 2025 Image credits: https://commons.wikimedia.org/wiki/File:TAR_Detour_clue.png https://commons.wikimedia.org/wiki/File:Carach_Angren_M%C3%A9an_22_08_200&hellip;

If you are looking for the slides from my PerfNow 2025 talk, Web Performance Allies, they are at speakerdeck.com/ethangardner...

Web Performance Allies - PerfNow 2025 Image credits: https://commons.wikimedia.org/wiki/File:TAR_Detour_clue.png https://commons.wikimedia.org/wiki/File:Carach_Angren_M%C3%A9an_22_08_200&hellip;

Here are mine: speakerdeck.com/ethangardner...

Just like web performance work, accessibility winds up being less expensive the earlier you implement it. Build accessibility in from the start, rather than bolting it on - make it part of the process.

@marcysutton.com #webperf #PerfNow #a11y

Wow! You're all in on the distance. I have about 50 races under my belt, but nothing over 10 miles. Good luck!

What distance? Have you run an obstacle course race before? They are so much fun.

performance.now(); 30th and 31st of October, Amsterdam On 30th and 31st of October, 2025, the sixth edition of performance.now() will take place in Amsterdam—a single track conference, covering today’s most important web performance insights.

performance.now() is coming!

@ethangardner.com will offer practical tips on presenting engineering data as a competitive advantage, a revenue driver, and a tool for enhancing user experience to help make performance optimization a strategic priority.

perfnow.nl/speakers.htm...

performance.sync() 2025 · Luma performance.sync() is a meet-up taking place on the evening before the performance.now on Wednesday October 29th! We are looking for speakers! Submit your…

performance.now() is coming!

The night before the conference, 29th of October, @mozilla.org organises performance.sync(), the pre-meetup where you can meet your peers to mentally prepare for two days of information overload. They're also looking for a few people to present.
luma.com/ziykhh4y

Come see me in Amsterdam! This lineup is loaded with great speakers in the #webperf community, and it's going to be a good time.

Episode 3 | PerformanceObserver - YouTube In this episode we have Andrea Verlicchi walking us through some real-world case studies of optimizing INP, and Ethan Gardner will discuss how to make allies...

The videos from our latest episode are up! Come catch a pair of great talks by @verlok.bsky.social and @ethangardner.com!

www.youtube.com/playlist?lis...

#webperf