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.

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...

Jquery 4.0.0 is out, great byte savings in the latest release #webperf

🆕 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

Anyone else seeing a degradation of Average Download time (+90ms ish) in Google Crawl Stats that started on(Around) September 24th? #webperf #crawler

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

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?...

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...

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...

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...

This article is such a gem! And the talk at Performance.sync() was too: youtu.be/E2E89NeBbEM?...

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/

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...

The new mPulse widgets with attributions for LCP, CLS and INP have made my performance checks more efficient and effective! #rum #cwv

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

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

Super interesting talk on advanced performance techniques from @timvereecke.bsky.social for #welovespeed. 🙌 www.youtube.com/watch?v=rjUr...

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

My new design will switch from 180px thumbnails to 48px ones! Great for #webperf, great for #UX 😂

A side- effect of #speculationrules is that CrUX shows a degradation in TTFB. Reason? CrUX unfortunately excludes TTFB from pre-rendered pages (subsequent navigations). As a result, the CrUX dataset for TTFB contains a relatively larger amount of slower landing pages. #webperf

We're excited to share that Mozilla and @wikimedia.bsky.social will once again be hosting a #webperf devroom at @fosdem.bsky.social 2025! The call for participation is open until December 1st. Find details on how to submit your proposal at wiki.mozilla.org/Performance/... #fosdem #cfp

Did you know if your load you LCP image from another origin (e.g. an image CDN) then LCP time may not be reported properly in RUM (but is in CrUX)? Let’s dig into why, and also how we’re looking to fix this very soon… 🧵

Quantifying user frustration with respect to web performance: blog.akamai-mpulse.com/blog/2024-11... new post on the mPulse blog. #perfmatters #webperf #rum

performance.now() 2025 will take place on 30th and 31st of October, 2025. #perfnow

@tunetheweb.com showcasing the power of the Speculation Rules API at #perfnow

#perfnow @jackfranklin.bsky.social will 103 Early Hints show up in the Performance Panel?

Took 2 mins at #PerfNow to talk about the RUM Community Group in W3C for anyone doing RUM. It's free and easy to join if you're interested! www.w3.org/community/ru...

"If you're using compression level 1, you're probably leaving stuff on the table, so increase it" - @paulcalvano.bsky.social at @perfnow.bsky.social #perfNow #webPerf

@programmingart.bsky.social now on stage talking about #webperf tools

@cliffcrocker.bsky.social summarising the Measurements and Metrics working group at the #webperf Unconference!

@derschepp.bsky.social in action at the #webperf unconference

Scalemates got a bit faster last month. #webperf

The all new performance chapter of the 2024 Web Almanac written by Jevgenija Zigisova and @inesakrap.bsky.social almanac.httparchive.org/en/2024/perf...

The potential performance gains of the new Speculation Rules API are heavily influenced by the eagerness level. Here is RUM data showing you the extra performance potential the Moderate option has compared to the Conservative level. #webperf #speculationrules

Planet Performance Calendar is a one-article-a-day Advent -style publication that runs in December since 2009, focused on Web Performance. If you (or anyone you know) want to share your experience, tool, research, rant with the #webperf community, please reach out calendar.perfplanet.com/contribute/