Harry Roberts
@csswizardry.com
🚀 Independent Web Performance Consultant • Speaker • Google Developer Expert, Web Performance • Accepting new clients • https://harry.is/for-hire
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Harry Roberts
@csswizardry.com
· Aug 8
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I’ve been writing or creating content in some form or another since 2009. Some of you have been with me since the very beginning. That over 15 years!The articles and research I publish on csswizardry....
csswizardry.gumroad.com
🧑💻 I wasn’t going to mention this until next week but it’s Friday—treat yourself!
I’ve just launched a members-only subscription: screencasts, Q&A, mentoring, discounts, and more.
👉 csswizardry.gumroad.com/l/subscribe
I’ve just launched a members-only subscription: screencasts, Q&A, mentoring, discounts, and more.
👉 csswizardry.gumroad.com/l/subscribe
Reposted by Harry Roberts
(Anyone traveling Schiphol to Centraal please be advised that Sprinter trains are anything but.)
🇬🇧 ✈️ 🇳🇱
To @perfnow.nl! My favourite week of the year.
To @perfnow.nl! My favourite week of the year.
October 29, 2025 at 11:42 AM
(Anyone traveling Schiphol to Centraal please be advised that Sprinter trains are anything but.)
🇬🇧 ✈️ 🇳🇱
To @perfnow.nl! My favourite week of the year.
To @perfnow.nl! My favourite week of the year.
October 29, 2025 at 9:25 AM
🇬🇧 ✈️ 🇳🇱
To @perfnow.nl! My favourite week of the year.
To @perfnow.nl! My favourite week of the year.
Reposted by Harry Roberts
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.
@csswizardry.com gets into which phones would work well, what emulations to use, and why it's important.
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.
csswizardry.com
October 28, 2025 at 10:02 AM
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.
@csswizardry.com gets into which phones would work well, what emulations to use, and why it's important.
Not only is @jpamental.bsky.social a really good friend, he’s an exceptionally good MC. You should hire him for your event.
October 21, 2025 at 9:19 PM
Not only is @jpamental.bsky.social a really good friend, he’s an exceptionally good MC. You should hire him for your event.
If your company has just laid you off, sneak `v` and `version` into the allowlist before you leave 👀
Allowlisted params (e.g. ?utm_source) can be reused in HTTP cache!
Blink: Intent to Ship: No-Vary-Search support for the HTTP disk cache
September 26, 2025 at 4:32 PM
If your company has just laid you off, sneak `v` and `version` into the allowlist before you leave 👀
Allowlisted params (e.g. ?utm_source) can be reused in HTTP cache!
Blink: Intent to Ship: No-Vary-Search support for the HTTP disk cache
Blink: Intent to Ship: No-Vary-Search support for the HTTP disk cache
Blink: Intent to Ship: No-Vary-Search support for the HTTP disk cache
groups.google.com
September 26, 2025 at 11:58 AM
Allowlisted params (e.g. ?utm_source) can be reused in HTTP cache!
.@tkadlec.bsky.social showed me this hyper elegant deep-link approach that @cloudflare.social provide: `dash dot cloudflare dot com/?to=/:account/:zone/speed/optimization/protocol`
This lets you select your Cloudflare account and zone before taking you to its correct Protocol dashboard!
This lets you select your Cloudflare account and zone before taking you to its correct Protocol dashboard!
September 24, 2025 at 12:24 PM
.@tkadlec.bsky.social showed me this hyper elegant deep-link approach that @cloudflare.social provide: `dash dot cloudflare dot com/?to=/:account/:zone/speed/optimization/protocol`
This lets you select your Cloudflare account and zone before taking you to its correct Protocol dashboard!
This lets you select your Cloudflare account and zone before taking you to its correct Protocol dashboard!
I recently started instrumenting both @cloudflare.social and browser cache hits/misses and the numbers, while obvious, are compelling. The best request is the one that never happens. Check that 0ms TTFB 😍
℅ @speedcurve.com
℅ @speedcurve.com
September 20, 2025 at 1:07 PM
I recently started instrumenting both @cloudflare.social and browser cache hits/misses and the numbers, while obvious, are compelling. The best request is the one that never happens. Check that 0ms TTFB 😍
℅ @speedcurve.com
℅ @speedcurve.com
Reposted by Harry Roberts
Build for the web, Build on the web, Build with the web.
An excellent take from @csswizardry.com on progressive enhancement, SPA frameworks and staying as close to the platform as possible.
csswizardry.com/2025/01/buil...
An excellent take from @csswizardry.com on progressive enhancement, SPA frameworks and staying as close to the platform as possible.
csswizardry.com/2025/01/buil...
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?
csswizardry.com
September 19, 2025 at 5:50 AM
Build for the web, Build on the web, Build with the web.
An excellent take from @csswizardry.com on progressive enhancement, SPA frameworks and staying as close to the platform as possible.
csswizardry.com/2025/01/buil...
An excellent take from @csswizardry.com on progressive enhancement, SPA frameworks and staying as close to the platform as possible.
csswizardry.com/2025/01/buil...
🔮 I held three of my 1:1s in the last 24hr and it’s amazing to see (and shape) what folk are working on. Different project, different audiences, different scales, but all so fun to help out with.
September 18, 2025 at 4:07 PM
🔮 I held three of my 1:1s in the last 24hr and it’s amazing to see (and shape) what folk are working on. Different project, different audiences, different scales, but all so fun to help out with.
I would wholeheartedly recommend this by the way. 2:1 salt:MSG used anywhere you’d use salt in a savoury context. Amazing on meat and green vegetables.
September 18, 2025 at 12:06 PM
I would wholeheartedly recommend this by the way. 2:1 salt:MSG used anywhere you’d use salt in a savoury context. Amazing on meat and green vegetables.
Huge news from @cloudflare.social! blog.cloudflare.com/the-rum-diar...
The RUM Diaries: enabling Web Analytics by default
We’re excited to announce the start of a major upgrade to Cloudflare’s performance analytics suite: Web Analytics as part of our real user monitoring (RUM) tools will soon be combined with network-lev...
blog.cloudflare.com
September 17, 2025 at 9:40 PM
Huge news from @cloudflare.social! blog.cloudflare.com/the-rum-diar...
What a privilege to be speaking at one of @adactio.com’s events! It’s only taken about 15 years…
Journal: Harry Roberts is speaking at Web Day Out
This line-up just gets better and better! You’ll want to be in Brighton on March 12th, 2026.
🔗https://adactio.com/journal/22135
This line-up just gets better and better! You’ll want to be in Brighton on March 12th, 2026.
🔗https://adactio.com/journal/22135
September 17, 2025 at 2:10 PM
What a privilege to be speaking at one of @adactio.com’s events! It’s only taken about 15 years…
Reposted by Harry Roberts
performance.now() is coming!
As tooling improves, is performance testing becoming any easier? @csswizardry.com, who spends every day auditing client projects,, thinks confusion has increased. Let's ensure that every test we run has a purpose and gives us useful data.
perfnow.nl/speakers.htm...
As tooling improves, is performance testing becoming any easier? @csswizardry.com, who spends every day auditing client projects,, thinks confusion has increased. Let's ensure that every test we run has a purpose and gives us useful data.
perfnow.nl/speakers.htm...
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.
perfnow.nl
September 16, 2025 at 4:12 PM
performance.now() is coming!
As tooling improves, is performance testing becoming any easier? @csswizardry.com, who spends every day auditing client projects,, thinks confusion has increased. Let's ensure that every test we run has a purpose and gives us useful data.
perfnow.nl/speakers.htm...
As tooling improves, is performance testing becoming any easier? @csswizardry.com, who spends every day auditing client projects,, thinks confusion has increased. Let's ensure that every test we run has a purpose and gives us useful data.
perfnow.nl/speakers.htm...
Friends and fans of Obs.js, please consider lending your vote for Interop 2026: github.com/web-platform...
Network Information API (connection) · Issue #1079 · web-platform-tests/interop
Description Short and sweet: I recently built Obs.js which taps into the Navigator API (chiefly navigator.connection) and surfaces device and network information. In Chrome, it’s a very powerful to...
github.com
September 15, 2025 at 4:40 PM
Friends and fans of Obs.js, please consider lending your vote for Interop 2026: github.com/web-platform...
I’ve spent a bit of the weekend doing some analysis of my newsletter and it’s blown me away. I’ve definitely been neglecting it. Over 4,000 of you with >55% open rate and >15% click rate. That’s way way WAY above the industry average. You folk are incredible! So supportive ❤️
September 14, 2025 at 12:01 PM
I’ve spent a bit of the weekend doing some analysis of my newsletter and it’s blown me away. I’ve definitely been neglecting it. Over 4,000 of you with >55% open rate and >15% click rate. That’s way way WAY above the industry average. You folk are incredible! So supportive ❤️
🪄 If you’ve ever wondered where the name CSS Wizardry came from (and why on earth it stuck), I’m telling newsletter subscribers the full back story later today: csswizardry.com/newsletter/
CSS Wizardry Newsletter – CSS Wizardry
Join the club!
csswizardry.com
September 14, 2025 at 8:44 AM
🪄 If you’ve ever wondered where the name CSS Wizardry came from (and why on earth it stuck), I’m telling newsletter subscribers the full back story later today: csswizardry.com/newsletter/
This is one of the best talks I’ve ever seen. Give it 20 minutes of your weekend.
Hey friends! I did a TEDx talk and it's now up on the TED Conferences YouTube. It's possibly the best and most important talk I've ever done.
I would ask that you watch it, and please SHARE it broadly and widely. Thank you! youtu.be/dVG8W-0p6vg #AI #Tech #TED
I would ask that you watch it, and please SHARE it broadly and widely. Thank you! youtu.be/dVG8W-0p6vg #AI #Tech #TED
Tech Promised Everything. Did it deliver? | Scott Hanselman | TEDxPortland
YouTube video by TEDx Talks
youtu.be
September 13, 2025 at 7:34 AM
This is one of the best talks I’ve ever seen. Give it 20 minutes of your weekend.
And if this interests you, I wrote about it OVER A DECADE ago: 24ways.org/2013/keeping...
When I was working on Obs.js, I had a private Git*Hub* repo for myself, and I added a secret Gist as a different remote for my subscribers to gain early access/preview versions.
September 8, 2025 at 1:13 PM
And if this interests you, I wrote about it OVER A DECADE ago: 24ways.org/2013/keeping...
I think a lot of folk tend to forget that @github.com Gists are Git repositories like any other, just lacking most of the GUI functionality. This means they’re a great place to store long-lived, version-controlled, distributed, shareable documents.
September 8, 2025 at 12:38 PM
I think a lot of folk tend to forget that @github.com Gists are Git repositories like any other, just lacking most of the GUI functionality. This means they’re a great place to store long-lived, version-controlled, distributed, shareable documents.
Reposted by Harry Roberts
Please stop inheriting the box-model. The supposed use-case for that is extremely out-dated, inheritance doesn't really help, and it actively makes real box-sizing use-cases more difficult!
This #CSS best practice was never the best to begin with:
www.oddbird.net/2025/09/04/b...
This #CSS best practice was never the best to begin with:
www.oddbird.net/2025/09/04/b...
Don't Inherit the Box Model
It's time to stop spreading this out-dated practice
www.oddbird.net
September 4, 2025 at 9:39 PM
Please stop inheriting the box-model. The supposed use-case for that is extremely out-dated, inheritance doesn't really help, and it actively makes real box-sizing use-cases more difficult!
This #CSS best practice was never the best to begin with:
www.oddbird.net/2025/09/04/b...
This #CSS best practice was never the best to begin with:
www.oddbird.net/2025/09/04/b...
🤝 If you were thinking about subscribing but think your boss should pay for it, there is a corporate tier: csswizardry.gumroad.com/l/subscribe?...
Subscribe
For over 15 years, I’ve been sharing practical, real-world insights on web performance. Free, open, and available to everyone. Now, I’m inviting you to join a new community of performance enthusiasts ...
csswizardry.gumroad.com
September 4, 2025 at 1:15 PM
🤝 If you were thinking about subscribing but think your boss should pay for it, there is a corporate tier: csswizardry.gumroad.com/l/subscribe?...
I just optimised a single interaction by 5× from 350ms down to to 70. This is an interesting one as it was caused by something designed to *improve* performance.
I made a six-minute screencast showing how I found and fixed it.
👉 Subscribers already know how: csswizardry.gumroad.com/l/subscribe
I made a six-minute screencast showing how I found and fixed it.
👉 Subscribers already know how: csswizardry.gumroad.com/l/subscribe
Subscribe
For over 15 years, I’ve been sharing practical, real-world insights on web performance. Free, open, and available to everyone. Now, I’m inviting you to join a new community of performance enthusiasts ...
csswizardry.gumroad.com
September 4, 2025 at 12:24 PM
I just optimised a single interaction by 5× from 350ms down to to 70. This is an interesting one as it was caused by something designed to *improve* performance.
I made a six-minute screencast showing how I found and fixed it.
👉 Subscribers already know how: csswizardry.gumroad.com/l/subscribe
I made a six-minute screencast showing how I found and fixed it.
👉 Subscribers already know how: csswizardry.gumroad.com/l/subscribe