Joan León

WebPerf Snippets started as a collection of snippets to paste into the DevTools console. With version 2.0, they are also built for AI agents to run webperf-snippets.net 🧵 #WebPerf #AI

With 2 years of rollouts, we've learned a lot about compression dictionaries and the Web. Patrick will cover what works, where the footguns are, how to maximize their effectiveness, and other experiments around compressing content on the web. @patmeenan.com at perfnow.nl

Sometimes custom solutions that we build highlight deeper challenges with performance and usability, and reveal an opportunity to grow the web’s native capabilities. How doe you move from patterns that work on one website to features that are built into our browsers? @scottjehl.com at perfnow.nl

Getting web performance prioritized is the hard part. I will talk about this topic on @perfnow.nl. How do you make the case for web performance? → Share your experience in this 3–5-minute survey: pagespeed.one/en/perfnow 🙏 #WebPerf #WebPerformance #PageSpeed

We now have LCP and INP sub-parts in @cloudflare-dev.bsky.social Real User Monitoring 🎉 This gives you deeper insight into where your websites and web applications are causing frustration for your users, so you can target changes more effectively. developers.cloudflare.com/changelog/po... #webperf

In this deep-dive session, Tim will use real-world data and performance metrics to show how scalemates.com became the fastest and largest scale modelling website in the world. You’ll leave with practical, actionable insights to push performance even further. @timvereecke.bsky.social at perfnow.nl

🚀 From population models to personalized AI! How can we build digital twins tailored to individuals? Join #GDGGirona on Oct 22 for a live demo exploring generative deep learning, transfer learning & personalized healthcare 👉 gdg.community.dev/events/detai... #AI #MachineLearning #DigitalTwins

Es todo un lujo poder formar parte de @a11yconf.com como ponente, donde hablaré de "El árbol de accesibilidad frágil: por qué el HTML semántico es clave para el rendimiento web" 🎟️ Aprovecha ahora que quedan entradas!!! 2026.a11yconf.com/entradas/ #a11y #WebPerf #a11yConf

Thank you so much @veneman.dev 🥰 Two awesome new stickers on my laptop from a great project: @projectwallace.com #CSS #CSSTools #WebPerfTools

JPEG XL shipped in Chrome 155 today, try it out! Huge kudos to Luca and team for getting this done. Image codecs are cool in so many levels, and I'm super impressed by the people who make that magic happen. developer.chrome.com/blog/jpeg-xl...

During a perf audit for a client, I read this in a PR: "The module should only be loaded once, not every time a file is selected." When I read it, something didn't add up, so I started digging. And the result surprised me. I wrote a post joanleon.dev/en/dynamic-i... #JS #WebPerf

How far ahead browsers fetch lazy images: • Chrome: 1,250px on 4G, 2,500px on 3G, 6,000px (!!) on 2G • Firefox: 600px, on any connection • Safari: one viewport. Lazy iframes: 0px, they wait until on screen

One thing I’m experimenting with for a performance audit: Using RUM data + @debugbear.com MCP to build synthetic tests based on how the product is actually used RUM → real user behaviour → MCP → representative synthetic tests www.debugbear.com/docs/mcp #WebPerf #RUM #MCP

The case against JPEG XL Investigating JPEG XL's place as a Web image codec, by @giannirosato.com, via @webperfreport.bsky.social giannirosato.com/blog/post/ca... #JPEGXL #JXL #ImagePerf #WebPerf

I added WebMCP to the GeeksCAT Conf 2026 website, so an agent can ask for the schedule, the speakers or the event details as tools instead of reading the HTML. It's a static Astro site, so I go through it layer by layer. joanleon.dev/en/webmcp-st... #WebMCP

We created Modern Web Guidance to bring web platform expertise right into your agent workflows. Have you tried pairing these skills with Chrome DevTools for agents to audit performance and automatically fix code? Check it out and join 10K+ web developers who are coding smarter → goo.gle/4yEVz1h

P75 is green: LCP 1.58s, INP 176ms, CLS 0.01. P90: LCP 2.68s, INP 352ms, CLS 0.17. 15% of visits get a noticeably worse experience. Product Performance doesn't end once you pass CrUX: if P75 is good, work on P90. #WebPerf #CoreWebVitals #RUM #ProductPerformance

⚡Featured posts this week: ✨ Submit your proposals for Interop 2027: @rachelandrew.co.uk ✨ Reading a performance profile: @nucliweb.net ✨ HTML over WebSockets: @androsfenollosa.bsky.social ✨ Intro to Web UX and Speed Optimization: @sergeyche.dev 🙏 Special thanks to the authors! #webperf

🤩 Fantastic article by @nucliweb.net on HTTP cache partitioning and the #CrossOriginStorage API: joanleon.dev/en/http-cach.... Try the embedded demos with the COS extension installed or in one of the experimental browser builds (see the Awesome Cross-Origin Storage list: github.com/tomayac/awes...).

⚡Featured posts this week: ✨ AI and organic search are doing different jobs: @kylerisley.bsky.social ✨ The CrUX 28-day rolling window: @nucliweb.net ✨ AI Web Readiness as a Curb-Cut: @ethangardner.com ✨ HTTP Integrity Digests: @simmervig.org 🙏 Special thanks to the authors! #webperf

I love the optimization: web, rendering, images, video, and now tokens. @lydiahallie.com published a great guide to Maximizing the value of your Claude Code sessions claude.com/blog/maximiz... #AIOptimization #AI #Claude

Reading a Performance Timeline by @nucliweb.net. This would be great for people who still have issues with Performance Timeline in Chrome. I love the form of this site. perf.reviews/profile-guide

Most skills are a Markdown file that grows out of control and gets loaded whole, even when the task doesn't need it. Modern Web Guidance inverts the pattern: 250 fixed tokens, and the agent retrieves the guide it needs on demand. joanleon.dev/en/modern-we... #AI #WebDev #CodingAgents

In my audits, the question I hear most after a deploy is "why hasn't CrUX moved yet?" The window is always 28 days; daily, weekly and monthly are just cadences over the same data. And p75 resists change by design I explain it with two interactive demos joanleon.dev/en/crux-28-d... #WebPerf #CrUX

A letter from @addyosmani.bsky.social arrived today, thanking me for my work on Agent Skills. I got in through web performance and stayed for the rest. Thinking about contributing to open source? Start small. Docs and honest reviews count. github.com/addyosmani/a...

While some people laughed about the number of dependencies in the JS world, others worked to improve the ecosystem (like @e18e.dev). Now many of my open source projects have around 20 packages in node_modules, including transitive dependencies.

⚡Featured posts this week: ✨ Is your site agent-ready?: @cloudflare.social ✨ Measuring soft navigations: @tunetheweb.com and @mmocny.com ✨ Reading a performance profile: @nucliweb.net ✨ The Absolute State of Management: @infrequently.org 🙏 Special thanks to the authors! #webperf

We got a few new individual sponsors recently in @e18e.dev - thank you to those of you who are supporting us 🙏 Getting sponsorships for a community is much harder than for a popular web app or dev tool. Every little helps. If you'd like to help us improve perf for all of us, check out our OC 🩵

In my audits, reading the Performance profile is where people get stuck: the flame chart and waterfall look like noise at first I built an interactive guide to make them click, every figure is interactive, plus LCP, CLS, INP and the Insights panel perf.reviews/profile-guide #WebPerf #DevTools

The curse of web performance - once you know it, you can’t unknown it and I see performance issues on the sites I visit too and can’t help it but open DevTools often as well. I was even thinking for creating a podcast-style Meet4SPEED YouTube channel looking at websites and improving them.

Modern UI Patterns, by @una.im at CSS Day 2026 www.youtube.com/watch?v=8FSL... #CSS #UI

I've been running #Antigravity Skills in real projects and the YAML frontmatter does much more than the docs show. kind: subagent + restricted tools + the right model per task. That trio makes agent behavior predictable and keeps costs in check. joanleon.dev/en/antigravi... #AI #AgentSkills