For the web dev nerds: meet `containertiming`! That's right, just an attribute! 🧵👇 You might have heard of elementtiming (and maybe also Server-Timing, performance mark/measure etc) already. `elementtiming` can be used for tracking image and text nodes (p, h1 etc) paint timings. 1/6

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 fix is already here! That's fast 🚀 Thank you @webkitgtk.org Team! Hopefully already there in next Safari release 🤓 bugs.webkit.org/show_bug.cgi...

With #CoreWebVitals data, we usually help agencies and merchants improve their sites and shops. But sometimes the data helps browsers too. An example: We recently spotted very inflated INP numbers across many sites on mobile (P75) specifically for `back-forward-cache` aka #BFcache navigations. 1/5

After implementing Compression Dictionaries back in December, I sat down with @yoav.ws and @patmeenan.com to discuss getting the most out of them and provide some visuals for those new to the concept. Check out the video below: youtu.be/YR2er3EiYnM / lessonsofacto.com/videos/032-c...

Using`preventDefault` within <dialog> close event causes mobile Chrome (but not Brave) to crash 😬 ``` document.body.addEventListener('command', (e) => { if (e.command === 'close') { e.preventDefault(); } }, { capture: true } ) ``` (crashing on v143 & 144 @ Android 13 & 16)

I learned this the hard way: the following works in #Chromium, but not in #FireFox ``` body *::scroll-button(*), body { display: none; } ``` Order of selector doesn´t matter. It seems like FireFox is tripping over it all together when encountering such selector @jakearchibald.com

(literally) breaking update: Is your site using #Facebook, like many others? Our RUM data shows it's breaking the #UX of.. all of them! According to our data of all our #RUM users, Facebook shipped an update on Dec 8th at 18:15 UTC. They started using the `unload` event again 😬 1/6

Look at that 🤩 Safari now supports #LCP and #INP as well! And we can clearly see it in our data 💪 Dates: 🗓️ Nov 3rd: Safari rolled out support in their 26.2 beta release 🗓️ Dec 12th: Safari released it to the public Huge update from the WebKit team, and for #CoreWebVitals in general 👏 1/3

Big update: both #LCP and #INP metrics (part of #CoreWebVitals) for #Safari has landed with the 26.2 release! 🤓 Well done @webkitgtk.org team! Great timing too now that we got our #Elastic setup sorted 💪 (earlier) blogpost: www.rumvision.com/blog/safari-...

Growing pains and performance gains explained: Our RUMvision.com query response times were -quite ironically- not as fast as we wanted them to be. We reached out to @elastic.co and queries became up to 140x faster. Scatter chart and percentile tables included: www.rumvision.com/blog/faster-...

Whoops, history repeating itself? 😬

Whoops, @cloudflare.social outage. And we're seeing it quite clearly in our Real User Monitoring (RUM) data: 📅 top: Nov 17th 10:30 - 13:30 CET 📅 bottom: Nov 18th, 10:30 - 13:30 CET (i.e. ) 1/4

#LCP and #INP support in #Safari really coming close now (maybe even in 2025?) as Safari 26.2 Beta Release Notes includes: - support for the Event Timing API - Largest Contentful Paint metric Great work by the #Webkit team! A blogpost: www.rumvision.com/blog/safari-...

#perfnow early morning performance session with @stuart-mcmillan.com (although he did a longer version 😅) Now on to the real event @ @perfnow.nl! 😍

@perfnow.nl Amsterdam weather update for those that haven't packed yet: Not too bad during the perf days as it will become slightly warmer + less rainy from Wednesday to Friday.

@andydavies.me need a LoAF image for your @perfnow.nl talk? I just ran into this at Schiphol 🤓😆 #LoAF #INP

Nerdy stuff! @mozilla.org #Firefox just enabled support for #INP with v144 🎉 I dived into our raw RUMvision data. And yep, can confirm that it works when using Google's web-vitals #JavaScript library 😍 (updated) article + chart + baseline badges in a blogpost: www.rumvision.com/blog/firefox...

Weekend! But also: looking back at quite the event, venue and community! I’ve only spoken to a purely #SEO audience a handful of times, but this one was truly energizing! A stable internet was needed to pull off the live quiz. Some attendees couldn’t even join in 😬 1/4

Aftermath sketch of our talk 🤩 Someone in the audience of which I thought was taking notes the old school way, appeared to have been making sketches 🤓 Huge thank you to Jeroen Heijmans for doing + sharing this! 1/2

New speaking gig confirmed: #SEOBenelux 🤟 Happening next week in between my 2 other scheduled talks this month! But this edition and talk will be different: → pure #SEO audience → bringing me back at another SEO event → this time in #Antwerp, October 10th 1/2

Many people don't know this: you can help shape the web with just an upvote (But: Today is the last day!) When I started frontend dev 20+ years ago, browsers felt untouchable to me: everything is set in stone and decided already. But over time (and especially since 2021) I learned that: 1/4

@fronteers.bsky.social speaking gig is coming up soon (Oct 3rd), but first: Visiting #MeetMagento Italy! 📍 happening in Rome 📅 Thursday September 25th ☕ Coffee break sponsored by RUMvision.com Travelling with @karlijnlowik.bsky.social as she will be talking about #sitespeed, #RUM, #memes + more

According to @httparchive.org 2024 research, 16% of mobile pages are still lazyloading their #LCP image! This could cost you a relation with customer! Fun fact: this percentage is kinda different from mobile data from sites using RUMvision.com (23%, see screenshot in 5th tweet) 1/6

We just added something nerdy to our tool, as treemaps seems to be hot in #JavaScript + web #performance world 🔥 When using RUMvision - Core Web Vitals monitoring to track #UX in real-time, we already show site owners a third party dashboard. But we now added a treemap-view as well: 1/4

My scariest talk ever? Probably this one, where we talked about a topic (#INP) at a sold out event with 10+ Googlers. And 9 of them being the authors of our subject. Imagine that! It's like explaining how to invest while Warren Buffett is sitting in the audience.. x9 😬 1/4

Paul Kinlan and @rachelandrew.bsky.social in their opening remarks, and (Paul) then covering "new in Chrome" at #GoogleIOConnect including #CoreWebVitals and #Baseline

At #GoogleIOConnect in Berlin! 🤘🚀

We overlaid collected #CoreWebVitals from our users (and their visitors) from #Spain + #Portugal with electricity usage chart from Red Eléctrica. We saw a strong correlation: [A] On April 27th and 29th, traffic dips after noon as a result of lunch time and possibly siesta 1/2

If you're reading this then please don't ever invest in #PageSpeed / #CoreWebVitals! By not investing, you: → get to keep that money in your business 👌 → will allow my current Core Web Vitals clients to actually do get the additional #SEO boost (as part of Page Experience ranking signal) 1/2

My last chance: doing a proof run with a Google webinar happening in exactly 2 days. With Tony Conway we'll be talking about: → #web #features and Can I Use → How the (relatively) new #Baseline project simplifies dev decision making → Existing and upcoming tools 1/2

Many of you might be like me: wanting to use new web features to improve hashtag#pagespeed, but without adding too much hashtag#JavaScript or (future legacy) polyfills 🤓 During audits, I've seen: 1️⃣ polyfills for responsive images (yes I know, very outdated) 1/5

Yesterday I was welcomed by Dutch Digital Agency Webreact @ their awesome office! 😀 With a group of 12, we went through all things #pagespeed: 1️⃣ #CoreWebVitals metrics 2️⃣ #Lighthouse vs #CrUX vs #RUM 3️⃣ WebPageTest & Chrome DevTools features 4️⃣ new browser APIs allowing us to use less JS 1/3

Client: "We don't have any non-JavaScript users" "No, all your users are non-JS while they're downloading your JS" I'm actually stealing a tweet from Jake Archibald (ex-Google, now @ Spotify) here: x.com/jaffathecake... Fun fact: 📅 Jake tweeted this a decade ago at May 28, 2012 1/4

We've updated our timelines for deprecating the unload event. We're looking to start ramping this up soon, starting with the most visited site—Google (nothing like eating your own dog food!) and then the other top 50 sites, followed by the general web. developer.chrome.com/docs/web-pla...

Awesome #CrUX update by the people from #Google (and also partially available in our free tool as well) 👏 This was added: → LCP image subparts → LCP resource types → Round Trip Time (RTT) tri-bins → RTT p75 and histograms We added #LCP resource type already as well (see attached). 1/4

First public gig of 2025 has been announced, and it'll be a sunny one! Together with @karlijnlowik.bsky.social I'll be hosting a workshop focusing on debugging #sitespeed & #CoreWebVitals issues via #WebPageTest, #RUM & #DevTools. General event info + tickets via: www.linkedin.com/showcase/hyv...

Few days ago, I asked people about Can I Use vs MDN. #Baseline was the least popular. Guess what? We adopted it anyway 🙃 So that: → when web features are mentioned, you'll now see browser support badges in our RUMvision blogposts and other pages 1/4

Browsers continue to come up with new features (WebP format and browser lazyloading) Sure, webp + lazyloading are two examples feel very old by now. And that's exactly my point! 1️⃣ How soon did you implement them 2️⃣ All while browsers keeps on giving (AVIF, Speculation Rules, View Transitions). 1/2

I could have spent time playing some PS during my Christmas break. But I decided to play with CSS #viewTransitions instead. Not just the basic #CSS, but applying a bit of tailored #JavaScript thanks to @bram.us his demos. Here are the results: 1/4

Don't deploy on Friday, that's lesson one. It's Friday 13th today - twice not fun! When bad luck doubles, don't take the risk, Wait for Monday - that's the safer fix! #ecommerce #deploy #noDeployFriday #FridayThe13th 😆

Just leaving this here: → as I'm still see this happening today 😬 → and so that I can link to this post when I'm running into yet another LinkedIn post with a 100% #Lighthouse, but actually just delaying all #JavaScript 🤓 𝐇𝐨𝐰 𝐭𝐡𝐢𝐬 𝐰𝐨𝐫𝐤𝐬? A dev uses a plugin that delays all JS for either: 1/3

This #CLS win stands for a difference between #CrUX and #RUM: It was the result of CrUX measuring all pagehits within an origin. Whereas RUM JS typically isn't deployed on admin pages. But GSC tried to attribute this to public pages, leaving us confused. 1/2

I had a blast, speaking at the 5th (and my 4th) @perfnow.bsky.social conference together with my colleague, CEO, bos, partner and wife @karlijnlowik.bsky.social We're not done yet, more talks and socializing to come Meanwhile, sllidesof our talk can be found here: www.rumvision.com/blog/perform...

Here we go! If you're here: feel free to engage with us on #RUM, #pagespeed, #CoreWebVitals and #Lighthouse topics. You'll find many RUMvision.com team members Jordy Scholing, Max Bronner and @karlijnlowik.bsky.social this 5th @perfnow.bsky.social web #performance conference.

Excited for upcoming web performance days with @karlijnlowik.bsky.social, colleagues Jordy & Max and many other performance enthusiasts at @perfnow.bsky.social! 🤓