Measure What You Impact, Not What You Influence – CSS Wizardry When implementing performance fixes, it’s imperative that you measure the right thing—but what is ‘right’?

It looks like you’re instrumenting a whole page reload…? Can you run something closer to the metal? csswizardry.com/2022/08/meas...

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

😂

Hah! That’s a decent little exploit actually. Gonna set all my posts a year in the future so I dominate your feed 😂

Haha nah, I wrote two pieces over the weekend and wanted to space them out a little date wise. I guess you’re an RSS user?

I miss #WebDayOut :(

I snuck it live a little early 🤫

reading: What Is CSS Containment and How Can I Use It?

csswizardry.com/2026/04/what...

— my prayers were answered! Harry explains all 🙏 for my next wish...

100% agree with this!

Browsers are AMAZING at loading a page in mostly the right way by default.

There are lots of extra options (fetchpriority, loading=lazy) to tweak that further if you know with reasonably certainly that they could benefit from those. If it’s ambiguous, then leave it be.

🚫 When All You Can Do Is All or Nothing, Do Nothing

For all you weekend warriors, advice for times of uncertainty.

csswizardry.com/2026/03/when...

Sunlit canal in The Hague with calm reflections, a white villa on the left, cyclists and parked bikes along the right-hand path, and a tram crossing a bridge in the distance under a clear blue sky

🇳🇱 Freshly back from a wonderful working week in The Hague. I shall never tire of this beautiful city.

Same! I guess at this rate I’ll catch you in… 2031? 😭

It was so so good to see you! What a pleasant surprise. Say hi to everyone for me!

Me gazing longingly at Jeremy while he introduces me on stage at Web Day Out.

Well, Brighton, you’ve been stunning as always. Thank you so much to @adactio.com and the @clearleft.com team for having me at #WebDayOut, an invigorating and inspiring shot in the arm to kick conference season off proper.

Have you headed home?

A photo of me on-stage taken from the vantage point of an audience member. I’m pulling a face that looks almost kind of lustful in a way. I’m actually glad you can’t see it—it isn’t flattering.

Me looking at standardised web APIs like…

#WebDayOut

Web Day Out 2026 – Photos by Marc Thiele This is my set of photos from Web Day Out 2026 in Brighton.

Hello and good morning from Brighton, where I attend #WebDayOut. If you want to follow along visually, here is my set of photos that document the day. More to follow. marcthiele.com/photos/web-d...

Build for the Web, Build on the Web, Build With the Web Every layer of abstraction made in the browser moves you further from the platform, ties you further into framework lock-in, and moves you further away …

Slides from my #WebDayOut talk, ‘Build for the Web, Build on the Web, Build With the Web’. Incredibly proud of this one.

speakerdeck.com/csswizardry/...

Jeremy Keith on stage introducing Web Day Out.

And we’re off! #WebDayOut

Hey, Bluesky! Have some blue sky.

I’m in beautiful Brighton for @clearleft.com’s #WebDayOut tomorrow. Who else is here?

I’ve been consulting for 12 years and I still get a real rush every time an enquiry comes in. An amazing feeling!

How to Think Like a Performance Engineer As awareness and tooling around site speed have been improving at a very exciting rate, has performance testing actually become any easier? Any more str…

speakerdeck.com/csswizardry/...

Build for the Web, Build on the Web, Build with the Web – CSS Wizardry What is the real, long-term cost of adopting a JavaScript framework?

Build for the Web, Build on the Web, Build with the Web

csswizardry.com/2025/01/buil...

I like the walk! Especially after being sat in lounges and planes. But I did spot the same route.

(Anyone traveling Schiphol to Centraal please be advised that Sprinter trains are anything but.)

I hope so!

Woohoo!

SmartWeb, Bucharest, September 2014!

🇬🇧 ✈️ 🇳🇱
To @perfnow.nl! My favourite week of the year.

Low- and Mid-Tier Mobile for the Real World (2025) – CSS Wizardry Discover the most representative low- and mid-tier mobile devices for web performance testing in 2025.

You know you should be testing your site or app with low and mid-tier mobiles, but what exactly does that *mean* for 2025? What's low-end? What's mid-tier? What are people using right now?
@csswizardry.com gets into which phones would work well, what emulations to use, and why it's important.