Yoav Weiss

If you ever struggled with understanding if your CSS performance issues are coming from style calculation or from layout, LoAF's styleDuration and layoutDuration is shipping in Chromium 158 to help with that groups.google.com/a/chromium.o...

Wrote a bit about why I think WebMCP matters: blog.yoav.ws/posts/why_we...

@43081j.com Hey! As you chimed in on github.com/webmachinele..., I thought you may have opinions on github.com/WICG/persist... Chrome folks are looking for people to play around with prototypes and provide feedback :)

We made Shopify storefronts faster with automatic Early Hints. By finding and preloading render-blocking resources, we improved p75 FCP by 76ms and LCP by 100ms. No merchant or theme changes required. performance.shopify.com/blogs/blog/f...

Heard of the Supporters of Chromium-Based Browsers (aka SoCBB)? No? Well, we at Microsoft came together with Meta, Opera, and Google to fund improving code, fixing bugs, interop issues in Chromium, so it stays healthy. Said another way: get paid to fix chromium bugs!

Right now, if you import something from JS, and the result is a 404 (or other not-ok status code), it fails the load & gives you nothing. I wonder with json imports, and maybe even text/byte imports, if that's the right pattern github.com/whatwg/html/...

Soft navigations Intent to Ship!! groups.google.com/a/chromium.o...

The Chrome DevTools team are doing a "papercuts" sprint where they try to address lots of small, irritating bugs and annoyances. Reply with crbug.com links (no bug, no fix—that's the deal!) and will see what we can do. No promises though as some may be features/too big/unclear how to solve.

PSA: Features available behind a feature flag have not shipped. (The thread had some more examples and words)

I'm proposing a way to be able to persist iframes across navigations github.com/WICG/proposa... Best idea or worst idea??

Speed still matters. "for every 100 milliseconds slower a store loads, conversion tends to be about 3.5% lower. (...) For every 32 milliseconds slower a store responds to interactions, conversion tends to drop by about 1.5%." www.shopify.com/enterprise/b...

Container Timing is a new browser performance API for measuring when an area of a web app has been displayed. It is available in an Origin Trial in Chrome 148 🎉 Read the blog post below to learn more 👇

I say it every year - if you're even the least bit interested or involved in web performance, this is THE place to be every year. It's the one trip I prioritize my travel budget for. The talks are awesome, but the hallway track is unbeatable. The concentration of experts in one place is insane.

I'm very excited about this! Have seen some really significant impact in our tests. With the sizes of websites and JS payloads continuing to increase, this is both important and impactful.

*web frameworks klaxon* If you work on a web framework then there is a w3c proposed community group: the Web Frameworks Community Group, a place for framework folk to feedback to browser vendors about what they want to see! If you want this it needs your support! www.w3.org/community/gr...

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...

Something I've been helping @yoav.ws with. A proposal to allow you to measure Speculation Rules API and <link rel=preload> usage. Are you over-speculating? Under-speculating? Until now you've only really been able to measure secondary impact, but with this proposal you'll can have better data.

Speeding up CSS with compression dictionaries. @yoav.ws shows how combining critical and full CSS via compression dictionaries cuts bandwidth and accelerates page transitions. Works now in Chromium. #performance #css calendar.perfplanet.com/2025/how-to-...

shout out to @frehner.me for adding name only container queries in Safari! bugs.webkit.org/show_bug.cgi...

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-...

We have Custom Elements, but do we also need Custom Attributes? This was discussed at TPAC. Is it something you'd like on the platform? https://github.com/WICG/webcomponents/issues/1029

Out-of-order HTML patching, another proposal from TPAC, lets HTML be presented non-linearly, and a single file can update multiple parts of the page. Would this feature be useful to you?

Compression dictionaries is now an official RFC! www.rfc-editor.org/rfc/rfc9842....

I'm proposing a change to iframes that will allow child frames synchronous access to data attributes on the parent frame. Let me know your thoughts: github.com/blittle/ifra...

✨ SPDY STREAM 011 ✨ w/ @krzksz.bsky.social & @yoav.ws After deploying the SPECULATION RULES API to their merchants, they join me this week to discuss the experience and their findings. Join us! (updated day and time) 📆 Thursday Sept 25 ⏰ 11am EST, 5pm CEST 🔗 bit.ly/spdy-stream-011

📝 Fetch streams are great, but contrary to popular belief, they're not good for measuring upload/downloading progress. ⬇️ Here's why, and how to avoid the gotchas ⬇️ jakearchibald.com/2025/fetch-s...

Great post and it's been a pleasure helping @krzksz.bsky.social and @yoav.ws get this working on Shopify. performance.shopify.com/blogs/blog/s...

Starting my new role on Monday. Could be anywhere.

today is my 40th birthday. to toot my own horn a bit, I'm the happiest, healthiest, and most successful I've ever been, so I'm going to indulge myself and do one of those "40 things that made me who I am" threads so buckle up (or mute me for the next little bit 😆)

Blink: Intent to Implement and Ship: Http cookie prefix

CSS uses a complex algorithm to decide how to animate transforms. If you get it wrong, as many folks do, you end up with an unnatural animation. Here's how it works, and how to avoid the pitfalls. jakearchibald.com/2025/animati...

In case anyone out there is looking for a good-first Chromium bug, issues.chromium.org/issues/42421... is one I'd be happy to mentor someone through..

What do y'all think of reviving <img lowsrc>? (as a data URI, used until the real image loads)

Great video! Hoping my “Bug Fixes” PR mentioned at 24:20 can make it into WebKit soon 😊

✨ How We Contribute To Browser Standards ✨ by @yoav.ws The 3rd of the presentations from the #SPDYmeetup 003. 🔸 Yoav shares how his career working on browsers and for browser vendors has now brought him to Shopify, enabling him to address possible shortcomings in standards 🎥 youtu.be/VEYxyNxfqG8

My take on coding LLMs: they have no understanding of concepts and just do pattern matching. But pattern matching goes a looooong way

✨ Speculation Rules, and Their Effect on Shopify Stores ✨ by @krzksz.bsky.social 🔸 As part of the Growth Services team, Mateusz talks about the team's long journey to implement Speculation Rules at Shopify and, the lessons learned along the way. #SPDYMeetup 🎥 youtu.be/8k2cGNjwJ3c

Avoiding the fomo this year by eagerly being a part of #perfnow in 2025. Tickets on sale now to help you avoid that fomo too. perfnow.nl/speakers.html

Forget the G7 ❌, this was the SPDY6 ✅: 🇵🇱🇺🇸🇪🇸🇨🇦🇬🇧🇫🇷. An assemblage of great global minds for last night's #SPDYmeetup in Toronto. Everything was as stellar as could be. @guaca.bsky.social @yoav.ws + @krzksz.bsky.social all delivered poigant presentations! 🏁 Recordings to be shared shortly. ✨🙏🏾✨

Import maps are a great way to minimize cache invalidation in your module tree. But up until recently, they had a ton of sharp edges. So we fixed them!! shopify.engineering/resilient-im...

@zachleat.com here's that blog post I promised shopify.engineering/resilient-im...

Would web devs use this? - subscribe to highly anticipated features (like Temporal) - get notified when they land in a new browser / become Baseline - via email, bsky, GitHub, Slack, whatever

📢 We Announced speakers for the TORONTO SPDY MEETUP 003: Performance At Shopify: Estela Franco 🇪🇸, Yoav Weiss 🇫🇷 and Mateusz Krzeszowiak 🇵🇱 will walk us through how Shopify is doing their part is helping merchants be fast, and STAY fast. 🎟️ JOIN US bit.ly/spdy_toronto_003

Latest Chrome (and Safari I think?) implement multiple import maps, which I think enables this behavior (thanks @yoav.ws ) I don’t think you have to do document.write() tricks to get it working, just inline it in html.

Imagine being a software developer named Claude

If you ever wanted to use `sizes=auto` and were bummed out about Safari/Firefox support, Shopify now got a polyfill for ya! github.com/Shopify/auto...

My process for writing blog posts using LLMs: * Outline the points I want to make * Ask an LLM to fill in the blanks * Start reading what the LLM wrote and throw it away because it's mediocre garbage * Write my own thing