While I’m a big fan of the Speculation Rules API, there used to be one major downside: prerendered pages ignored loading=lazy, causing all images to download. That changed 2 months ago.
Tim Vereecke
@timvereecke.bsky.social
Loves speeding up websites. Web performance architect @Akamai, also runs https://www.scalemates.com #WebPerf #PageSpeed #SEO
New speed record 🚀 Just measured a 15ms Largest Contentful Paint (LCP), the fastest (prerendered) navigation I’ve seen so far on my website using RUM. #webperf
Sometimes, legacy applications use POST instead of GET to retrieve data. On Akamai, you can easily force caching of specific POST responses to improve both offload and performance. In the screenshot below, you can see the first (slow) and subsequent data retrievals using POST (fast, cached).
From Chrome 145 (on general release next week!), DevTools we will start to show so called "soft" navigations and "Soft LCP" in the Performance Panel traces. These are for SPAs which don't do a full page load, but instead "fake it" by updating the current page and pushing a new history entry. 1/5 🧵
Think prefetch is not enough, but prerender is too risky for your site? Well then check out "prerender until script"—a new option we're testing for the Speculation Rules API now available for you to test on your site with an origin trial! developer.chrome.com/blog/prerend...
Speculation rules prerender until script origin trial | Blog | Chrome for Developers
Learn about the new prerender until script option for the Speculation Rules API, now available in origin trial.
developer.chrome.com
🆕 The 202511 Chrome User Experience (CrUX) release is now live on BigQuery! Check out the announcement post for the full info: groups.google.com/a/chromium.o... Highlights below 👇 🧵 1/3
The new SVG hack? (Context: The lack of preconnect/preload means there is 0.000 performance impact for the user) Gaming the system? Lack of knowledge? Or is there a benefit not linked to #webperf? Heard about this at @perfnow.nl
103 Early Hints is now supported by more than 92% of all users. When done right, it is a great way to improve your higher percentiles of FCP and LCP #webperf
Scalemates was used by @tunetheweb.com as an example of how fast a site can be using the Speculation Rules API. It has an LCP of 483ms at the P75! #webperf
Why is my site fast? 55% of my pageviews on Desktop are coming from Bfbache or had an early start with Prerendering. 👌 #webperf is easy* in 2025 (*I know I know)
Unattributed Navigation Overhead (UNO) calendar.perfplanet.com/2024/uno/ by @timvereecke.bsky.social #WebPerf #Performance
Unattributed Navigation Overhead (UNO)
I promise you, UNO (Unattributed Navigation Overhead) is the best Christmas present you will get this year! UNO, not the card game, is the missing piece for many of your unsolved performance puzzles...
calendar.perfplanet.com
Why is my site fast? 55% of my pageviews on Desktop are coming from Bfbache or had an early start with Prerendering. 👌 #webperf is easy* in 2025 (*I know I know)
Amazing (and simple) technique by @kilianvalkhof.com . autofocus is a great way to make your login/registration and password reset forms more user-friendly htmhell.dev/adventcalend... I implemented it during my lunch break... so much better! #UX #htmhell
Great stuff. I just watched a talk from @timvereecke.bsky.social that covered the redirects, and I was surprised how big an impact they can have on TTFB. Time to track redirects in my RUM data (when possible). youtu.be/E2E89NeBbEM?...
Tim Vereecke at performance.sync()
YouTube video by Web Conferences Amsterdam
youtu.be
They should invent a CLS score for slide decks! #webperf #presentations
Hmm, interesting - looks like Chrome added support for the ORIGIN frame for HTTP/3 (eliminating the need for a DNS lookup before coalescing connections). blog.chromium.org/2024/12/maki...
Making Chrome QUICer
In October 2020, Chrome enabled HTTP/3 by default . HTTP/3 ( RFC 9114 ) runs over IETF QUIC ( RFC9000 ). Default-enabling HTTP/3 in Chrome ...
blog.chromium.org
Have you ever noticed unexplainable performance degradations? Unattributed Navigation Overhead (UNO) is probably the missing link. Watch my Lightning Talk from the performance.sync() meetup in Amsterdam! #webperf #rum #ttfb #cwv www.youtube.com/watch?v=E2E8...
Tim Vereecke at performance.sync()
YouTube video by Web Conferences Amsterdam
youtube.com
Web performance calendar day 28 with Tsvetan Stoychev's curriculum for teaching Real User Monitoring. Cup of rum? Sign me up! calendar.perfplanet.com/2024/wait-wh...
Wait? What? Web Performance Optimization is being studied in universities?
TL;DR: In this article I am sharing the good news that Web Performance Optimization is being studied in universities and I am laying out the plan of teaching Real User Monitoring which I will do for t...
calendar.perfplanet.com
This article is such a gem! And the talk at Performance.sync() was too: youtu.be/E2E89NeBbEM?...
Tim Vereecke at performance.sync()
YouTube video by Web Conferences Amsterdam
youtu.be
Stoyan Stefanov @stoyan.me · 2y agoWeb performance calendar day 21 with @timvereecke.bsky.social giving us the gift of UNO (Unattributed Navigation Overhead) - an insight into the blind spot gaps between TTFB components calendar.perfplanet.com/2024/uno/
Web performance calendar day 21 with @timvereecke.bsky.social giving us the gift of UNO (Unattributed Navigation Overhead) - an insight into the blind spot gaps between TTFB components calendar.perfplanet.com/2024/uno/
Unattributed Navigation Overhead (UNO)
I promise you, UNO (Unattributed Navigation Overhead) is the best Christmas present you will get this year! UNO, not the card game, is the missing piece for many of your unsolved performance puzzles...
calendar.perfplanet.com
Ready to make your sites load like 🚀? Join our latest livestream with @timvereecke.bsky.social where we dive deep into the Speculation Rules API! 🎥 What’s in it: - Pre-rendering & Prefetching Magic - Real-World Use Cases - Simple to complex use-case Catch the action on YouTube: dub.sh/MyXjkeC
Here's my idea for Vital Score: • shows % of traffic passing CWVs • no weights, shows the progress, easy to compare, evolves CWV assessment • formula: (LCP+CLS+INP+ min(LCP, CLS, INP)) / 4 What do you think? #webperf Thx @timvereecke.bsky.social for min() trick and @csswizardry.com for CrRRUX
This Friday afternoon I'll be at the Boston Web Performance meetup giving my talk on "Performance Mistakes". If you are in the Boston area and interested in web performance, join us! www.meetup.com/boston-web-p...
Performance Mistakes, Fri, Dec 6, 2024, 4:30 PM | Meetup
December's meetup will feature Paul Calvano, on his return from the PerfNow conference in Amsterdam. **Agenda** * 4:30 pm: Arrive & networking * 5:00 pm: Talk starts * 5:
meetup.com
My #wls2024 talk is available! I delved into advanced tuning techniques to make a modern website lightning fast. Using lots of charts and data, I showed how they helped make scalemates the fastest (and largest) modeling website in the world. www.youtube.com/watch?v=rjUr... #webperf
Beyond the basics, pushing the limits of webperf — Tim Vereecke
YouTube video by We Love Speed
youtube.com
My talk from this year's We Love Speed is on YouTube! 👇 In "Tight Mode: how browsers REALLY load web pages", I take a very deep/very nerdy dive into why browsers sometimes intentionally delay loading resources, why they all do it differently, and why they should *stop clowning around* 🤡 #webperf
How browsers REALLY load Web pages — Robin Marx
YouTube video by We Love Speed
youtube.com
Super interesting talk on advanced performance techniques from @timvereecke.bsky.social for #welovespeed. 🙌 www.youtube.com/watch?v=rjUr...
Beyond the basics, pushing the limits of webperf — Tim Vereecke
YouTube video by We Love Speed
youtube.com
The simplest view transitions example is a bit boring after a while! Something more fancy is complex! "auto" should ideally show different transitions based on the directory of the "old" vs "new" - /a/ » /a/b/ - /a/b/ » /b/ - /a/1.html » /a/2.html - /a/b/3.html » /d/e/f/4.html @bram.us