Harry Roberts

🎞️ Here’s an example:

🎥 I spent a few hours recording a bunch of short-form web performance tips and tricks on Sunday. I plan to continue recording and releasing as I encounter fascinating real-life scenarios. Interested?

Let me know if I can help!

Thanks!

I’m working with a client who has a very diverse (adverse?) customer base, so we’re sending off some more high fidelity Network and Device information to @speedcurve.com:

YouTube video by Harry Roberts Yorkshire Air Ambulance Site-Speed Optimisation

If you ever wondered what my Fix It Fast service (csswizardry.com/performance-...) looks like, it looks exactly like this:

youtu.be/da7hmM4aYDg?...

You can’t park there, mate.

I added an update about your change 👍

For me, personally, DevTools and many of the performance APIs.

Amazing! Thanks dude! I hope I didn’t sound critical?!

Making Sense of the Performance Extensibility API – CSS Wizardry Making sense—and use!—of the new Performance Extensibility API in Chrome DevTools.

📖 Making Sense of the Performance Extensibility API

csswizardry.com/2025/07/the-...

I went in pretty deep on this…

Wow

Would anyone like me to write this up? Demystify it a little?

Screenshot of Chrome DevTools’ Performance panel showing a custom track titled ‘csswizardry.com — custom track’, with a nested group ‘Technical Timings’. Within the group are three visible timing bars labeled `headTime`, `cssTime`, and `contentTime`, each rendered as light purple horizontal spans. Below this custom track is the ‘Main’ thread track, displaying standard task activity.

<script> performance.mark('headEnd'); performance.measure('headTime', { start: 'headStart', end: 'headEnd', detail: { devtools: { dataType: 'track-entry', trackGroup: 'csswizardry.com', track: 'Technical Timings', tooltipText: 'Head Tags Parsed', color: 'secondary-light' } } }); </script>

The syntax is pretty cumbersome, but the Extensibility API is worth looking at for any longer-term instrumentation.

from a web performance perspective, nothing inspires me more than a @csswizardry.com article!

Thanks!

Yeah I can’t help there I’m afraid 😂

Any other feedback about your experience with the site would be cool! Anything we can improve?

Setting a New Standard for ISO.org – CSS Wizardry How I helped ISO.org achieve all-green Core Web Vitals for the first time ever. LCP down 29%, CLS down 94%.

👀 CASE STUDY: How I got ISO.org to all-green Core Web Vitals for the first time… ever. csswizardry.com/case-studies...

Setting a New Standard for ISO.org – CSS Wizardry How I helped ISO.org achieve all-green Core Web Vitals for the first time ever. LCP down 29%, CLS down 94%.

📖 Some light reading for your Sunday. See what I did for ISO.org: csswizardry.com/case-studies...

AI won’t replace developers, it’ll replace typists.

Same same. General consensus is AI summaries stealing clicks.

Thank you!

Subscribe to Harry Roberts on Gumroad Web Performance tools and resources.

🎂 Today is my 35th birthday! To mark the occasion, the code 35 will get you 35% off anything here: csswizardry.gumroad.com

👀 Show, don’t tell!

I’m pitching to a lukewarm prospect. They’re suffering with INP (a lot!) and they know it, so they don’t need me to give them the numbers. Instead, I built them a demo so they could feel the problem for themselves. Far more compelling.

Core Web Vitals on iOS – CSS Wizardry Arrange a one-day workshop and get hands-on with Core Web Vitals in Safari

📱 Safari has promised us LCP and INP in 2025! Are you prepared? csswizardry.com/workshops/co...

SpeedCurve | Performance Hero: Harry Roberts Harry makes huge brands fast, and then generously shares his insights with the community. Thank you, Harry!

Happy to announce the @speedcurve.com #perfhero for the month of June, Harry Roberts! @csswizardry.com I had a catch up with Harry and talked all things webperf. Have a listen! www.speedcurve.com/blog/web-per...

I swear you’re still only 21. Congratulations, you two!

Assuming the latter (the only one that makes sense), it would flatten it out. Just like a rel=stylesheet would have done from the outset