Web Performance Calendar day 26 with Sébastien Mischler on HTML streaming/flushing and how this old trick (featured in the first edition of the calendar) applies to today's CSR world. Show content now, not after JS finishes thinking. Fast pages, happy users. calendar.perfplanet.com/2025/revisit...

Web Performance Calendar X-mas edition with Nicolas Hodin on BFCache: a huge UX win, but easy to break with Cache: no-store, unload handlers, iframes, or long-lived connections calendar.perfplanet.com/2025/chasing...

New blog post "Lazy-Loading Optional Fonts with Native Browser API" describing a wee trick I do on sightread.org to load music glyphs, optionally highperformancewebfonts.com/read/lazy-lo...

I’m using No-Vary-Search in production already—you probably should be too! @tunetheweb.com has the details 👇🏻

This one got released rather quietly and I think could do with a bit more attention! Read about how to avoid caching performance penalties due to tracking query params and the like!

Web Performance Calendar day 24 with @programmingart.bsky.social on TTFB. Yes, it's one of those X-mas Eves where we cuddle by the fire, drop everything and immerse into re-learning and re-evaluating what we thought we knew about a concept we use daily calendar.perfplanet.com/2025/ttfb-do...

Web Performance Calendar day 23 with @tunetheweb.com on configuring caches to ignore non-content-affecting URL parameters and reclaim performance. No more of this query string = cache miss nonsense. calendar.perfplanet.com/2025/fixing-...

Web Performance Calendar day 21 with Conor McCarthy and lessons learned from web perf client site reviews calendar.perfplanet.com/2025/insight...

Web Performance Calendar day 20 with @verlok.bsky.social on CLS-friendly skeletons. Can you "load more" while keeping layout shifts to a minimum? calendar.perfplanet.com/2025/optimiz...

Web Performance Calendar day 19 with Alex Podelko on how performance engineering has evolved with computing: from mainframes to distributed systems, web/mobile, cloud, AI. Knowing your history may help reduce wheel-reinvention and encourage skills reuse calendar.perfplanet.com/2025/a-short...

Web Performance Calendar day 18 with Amrik Malhans on breaking down LCP to pinpoint what's slowing down the page exactly and where to focus your UX-optimizing efforts calendar.perfplanet.com/2025/the-ana...

Web Performance Calendar day 17 with Adam Zachary Wasserman on outperforming modern frameworks with this one weird little trick calendar.perfplanet.com/2025/the-old...

Web Performance Calendar day 16 with @sandervs.bsky.social on why the word "millisecond" doesn't belong in the boardroom calendar.perfplanet.com/2025/why-we-...

Web Performance Calendar day 15 with @nicj.net, @cliffcrocker.bsky.social and @karlijnlowik.bsky.social Löwik presenting an update on W3's RUM Community Group and YOU calendar.perfplanet.com/2025/rumcg-a...

Web Performance Calendar day 14 with Morgan Murrah on compositing for smooth web animations and how GPU-friendly properties (transform, opacity) keep animations off the main thread calendar.perfplanet.com/2025/a-tale-...

Web Performance Calendar day 13 with Yoav Weiss (@yoav.ws) showing us a clever and creative way to ship *only* critical/necessary CSS for each page type (home, search, etc) while also avoiding duplicate code in the CSS bundles. calendar.perfplanet.com/2025/how-to-...

Web Performance Calendar day 12 with @adevnadia.bsky.social's investigation of React Server Components, their pros and cons compared to client-side rendering and traditional server-side rendering (with/without data fetching with/without Next.js) calendar.perfplanet.com/2025/intro-t...

Web Performance calendar day 10 with yours truly using ML and HTTPArchive data to explore an "AI webperf consultant" idea. YSlow (pronounced “Why Slow?”) meets aiSlow (pronounced “Eh, I Slow?”). calendar.perfplanet.com/2025/aislow/

Web performance folks, the pipeline of the advent calendar is dry. If you were thinking of writing or you've started, now would be perfect time to wrap it up and send it over. Thanks a million to everyone who'd helping! If you don't know what I'm on about, see calendar.perfplanet.com/contribute

Web Performance day 10 with Michal Matuška on what's new in React perf: <Activity> for stateful hidden UI and the Performance Tracks in DevTools for full-timeline visibility of what React is doing calendar.perfplanet.com/2025/react-1...

Hello London!

100ms ≠ 1%, do not trust the case study from Amazon Rather have a few high-quality case studies than many low-quality ones. It hurts the whole industry. My article for #WebPerf Calendar 2025. Thanks @stoyan.me! calendar.perfplanet.com/2025/the-inc...

Web Performance Calendar day 9 with @machal.bsky.social on Web perf folklore vs. evidence. Too many anecdotes (like 100ms = 1%) conflate speed gains with redesigns, UX changes, or seasonal shifts. Repeating them hurts the credibility of real performance work. calendar.perfplanet.com/the-inconven...

Web Performance Calendar day 8 with Edwin Molina Hernández @webperfreport.bsky.social showing how a great perf report is more than numbers, it turns metrics into actionable answers to questions like "what improved?", "what regressed?", and "what to do next?". calendar.perfplanet.com/2025/the-ana...

Web Performance Calendar day 7 with @fabkru.bsky.social showing us how the discipline of web performance in 2025 is evolving: from optimizing the past, to predicting and delivering the future. calendar.perfplanet.com/2025/web-per...

Web Performance Calendar day 6 with Aaron T. Grogg (@aarontgrogg.com). What if I told you that you need low-to-no JavaScript for interactive UI elements such as accordions, auto-expanding or auto-suggestion inputs, modals, hamburger menus and even more... calendar.perfplanet.com/2025/nolojs-...

Web Performance Calendar day 5 when @myshov.bsky.social shows us how to move heavy image decoding off the main thread. Drawing images in <canvas> freezing your UI and causing long tasks? Not anymore! calendar.perfplanet.com/2025/non-blo...

Web Performance Calendar day #4 when @denodell.bsky.social shows us how to adopt a fast-by-default mindset to escape the vicious cycle of ship-complain-panic-patch. calendar.perfplanet.com/2025/fast-by...

The event start in 30 minutes...and counting

Web performance calendar day 3 when @ethangardner.com shows us how to train a ML model on synthetic perf metrics and use it to predict approximate field data before a page/feature goes live. calendar.perfplanet.com/2025/traffic...

Tomorrow, 8am Pacific time

Bug or a feature: selecting code in the devtools console makes some tokens black rather than white?

bsky.app/profile/perf... exists now in the world

Woo boy - some of the examples in this post! www.debugbear.com/html-size-an... is nice solution to identify this though!

Web Performance Calendar day 2 with Matt Zeunert (of @debugbear.com) exploring large HTML documents in the wild. Larger document means more content, right? Or does it? calendar.perfplanet.com/2025/explori...

Web Performance Calendar'25 day 1 with @mb21.bsky.social on HTTP streaming in the world of HTTP2/3 and Node. Mauro shows us how to start rendering earlier, turning a slow (full) page load into a progressive experience using db.stream() in JavaScript calendar.perfplanet.com/2025/improve...

For the performance minded: it's Dec 1. This means that the *Planet Performance* Web Performance Calendar is looking for contributors. It's been going since 2009. Working on something? Case studies? Pls share! All the info is below. Curated by @stoyan.me ! calendar.perfplanet.com/contribute/

December is here (in a few hours in my timezone), which means the Web Performance "Advent" Calendar is back for its... 17th Edition! One article a day in the month of December. Be a part of it and contribute an article: calendar.perfplanet.com/contribute/

TGIF: I'm having some guests join me on Wednesday Dec 3rd to talk about Core Web Vitals. I revealed the 1st set of presenters today, and will reveal the others on Cyber Monday. Nonetheless, join us, @stoyan.me @cdaveross.bsky.social + a few more... 📆 Wed Dec 3rd ⏰ 11a EST 5p CET 🔗 bit.ly/cwv-summit

There needs to be a new branch of Mathematics that specializes in online hotel booking arithmetic. Like: 3 nights * $150/night */±{magic} = $738.79

In Seattle taking off for Los Angeles. Thank you everyone at #perfnow for the good times in the last few days!

There's a sight to see, freshly published in time for #PerfNow. Talk by @tunetheweb.com , an excellent walkthrough on how to get the most out of a truly powerful tool www.etsy.com/codeascraft/...

Interesting! Etsy implemented speculation rules and got these results: 👍 Time to First Byte on the listing page improved 23.6% 👍 First Contentful Paint improved 20.7% 👍 Largest Contentful Paint improved 21.1% 👍 DOMContentLoaded improved 20.4% #PerfNow #webperf www.etsy.com/codeascraft/...

Fellow #perfnow fellows, a reminder that PerfPlanet calendar is coming this December for another edition. And it needs YOU. Please ask if you have any contribution ideas or concerns calendar.perfplanet.com/contribute/

I co-wrote a post on the Etsy engineering blog about implementing Speculation Rules API (SRA) to prefetch product listing pages from search results. And many thanks to @tunetheweb.com and @cdaveross.bsky.social for the help and support! www.etsy.com/codeascraft/...

perforomance.run() everybody! The latest API available to folks visiting for #perfnow

New blog post which talks about building a new project/app without a build process www.phpied.com/import-javas...

Boarded the LAX -> AMS flight on the way to @perfnow.nl Few tickets are still available, if anyone forgot THE web performance event of the year is happening this Thursday and Friday, Oct 30 and 31st

Yey!

meet me in 15 minutes performanceobserver.dev/events/episo...