@nucliweb
Account based inSpain
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⚡️ Web Performance Artisan at @perfreviews_ | @GoogleDevExpert in #WebTech | @cloudinary Ambassador
Girona, Catalunya
Joined August 2008
- Tweets21.5K
- Following4.3K
- Followers12.1K
- Likes46.9K
Pinned Tweet
I have published a website with Web Performance Snippets to make it more user-friendly, more orderly, and with a search feature
⚡️💾 webperf-snippets.nucliweb.ne…
#WebPerf #Performance #PerfTools
Joan León 🏞️⚡️ retweeted
La #GeeksCAT2026 ja és història, i quina història! ⚡
Sala plena a L'Estació Espai Jove, 10 ponències d'altíssim nivell tècnic, debats sans i retrobaments amb la comunitat tecnològica a Girona.
Obrim fil amb el resum i agraïments 👇🧵
#GeeksCAT #Girona
ALT Foto de grup de l'equip d'organització, suport i els 10 ponents de la GeeksCAT Conf 2026 somrient a l'escenari de L'Estació Espai Jove de Girona al final de la jornada.
Joan León 🏞️⚡️ retweeted
Una xarrada de @carlesnunez de rendiment, de les que li agraden al nostre company @nucliweb ☺️
#GeeksCat #GeeksCatConf
Joan León 🏞️⚡️ retweeted
We gave Claude Opus 5.5 an article we wrote a few months ago and asked it to turn it into an animation.👇
📖 The Anatomy of a Web Performance Report
calendar.perfplanet.com/2025…
Thanks for the idea, @addyosmani !
#AI #ClaudeAI #WebPerf
Joan León 🏞️⚡️ retweeted
Claude Opus 5.5 drew each frame of this animation in JavaScript. Here's "how browsers work" in 40 seconds.
Joan León 🏞️⚡️ retweeted
AI Reporting Workflow ✨
Turn one WebPerformance Report into:
→ UX & SEO Audits
→ Benchmarks
→ Cross-report correlations
→ Executive summaries
→ Tickets & tasks
→ And much more
WPR Report → AI → Insights → Action
Use ChatGPT, Claude, or Gemini.
Link in comments 👇
Joan León 🏞️⚡️ retweeted
🎇 I made a small Chrome extension: a side panel that drives any site's WebMCP tools with Jev!
When you type, on every keystroke it picks the relevant page's tool, fills in the arguments, and tells you how sure it is.
Here it is grocery shopping:
Joan León 🏞️⚡️ retweeted
Kodak images are old film based images with blur, film grain and lack of resolution. The corpus was then scanned from film to digital using the scanner technology from late 1980s or very early 1990s.
This is not a way to benchmark modern codecs.
If you compare with a high quality digital corpus you will get different numbers.
Joan León 🏞️⚡️ retweeted
Reminder: Claude Code can test if a skill or plugin actually improves Claude's answers.
> claude plugin eval init
Tell Claude what a good result looks like in your plugin's folder and it writes the test cases for you.
> run claude plugin eval .
Joan León 🏞️⚡️ retweeted
🔮 Built a real-time click prediction right over the DOM using JEV that feels like a crystal ball.
Powered by jev-latest to predict the next clickable element and intent in 345ms per check, highlighting candidate elements on screen.
It's extremely cheap to use and helps predict user intention, hitting 83% accuracy in testing.
Usages that come to my mind:
- Web performance optimization via predictive resource load
- UX Research and testing
- Progressive UI loading based on intention
- Accessibility for reduced motor precision (highlight based on intention allowing to click, for example)
- And probably many more...
Joan León 🏞️⚡️ retweeted
⚡Featured posts this week:
✨ New ad metrics in CrUX: @alextcone
✨ The case against JPEG XL: Gianni Rosato
✨ Why Spotify Is Not Using Bayesian A/B Testing: Mattias Frånberg, Mårten Schultzberg
✨ International SEO: Barry Adams
🙏 Special thanks to the authors!
#webperf
ALT WebPerformance Report performance email preview highlighting optimization scores, Perf Links, and Core Web Vitals metrics on a colorful gradient background.
The case against JPEG XL
Investigating JPEG XL's place as a Web image codec, by Gianni Rosato, via @WebPerfReport
giannirosato.com/blog/post/c…
#JPEGXL #JXL #ImagePerf #WebPerf
ALT A dark-themed line chart titled “SSIMULACRA2,” showing BD-Rate (%) versus encoding speed in milliseconds for several image codecs. Colored lines compare codecs including AOM, JPEG XL, aperture-alpha, Iris-WebP, libjxl, SVT-AV1, and libwebp, with labeled data points. Most curves show higher BD-Rate at slower speeds, while some reach negative BD-Rate at faster speeds.
Joan León 🏞️⚡️ retweeted
Agent: *screenshots the page*
Agent: *scrolls*
Agent: *screenshots again*
Agent: *clicks the wrong button*
Agent: *screenshots again*
Page with WebMCP: hi, here are the 4 things you can do here, with descriptions
Agent: oh thank god
Joan León 🏞️⚡️ retweeted
Modern Web Guidance v0.0.187 brings new and updated guides and Codex plugin support → goo.gle/4harAXQ
✨ New guides: progress rings, scrollspy nav menus, loading spinners
📝 Updated guidance to avoid bfcache breakage and unwanted inline layout gaps
🔌 Added plugin manifest support for Codex
Joan León 🏞️⚡️ retweeted
10,000 installs and counting! 📈 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
An agent shouldn't have to guess CSS selectors to read a conference schedule.
I implemented WebMCP on the GeeksCAT Conf 2026 website: a static Astro site, no server.
joanleon.dev/en/webmcp-stati…
#WebMCP
Joan León 🏞️⚡️ retweeted
Open up your app's inner workings to AI agents with custom tools in DevTools for agents→ goo.gle/4r5H3x7
Write plain JavaScript to build tailored third-party tools that save tokens and bypass manual steps like login forms built for humans.
Joan León 🏞️⚡️ retweeted
🔥 It was an absolute pleasure to talk about WebMCP among other AI on the web topics with @domfarolino on the latest @syntaxfm!
Along with the rest of the internet, @wesbos and @stolinski are heroes of mine. Thank you for hosting us!
youtube.com/watch?v=xtVvkRTH…
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 #ProductPerformance
ALT DebugBear RUM dashboard showing Core Web Vitals at the P75 percentile: Largest Contentful Paint 1.58s, Interaction to Next Paint 176ms, and Cumulative Layout Shift 0.01, all flagged green on the score bar.
ALT DebugBear RUM dashboard showing Core Web Vitals at the P90 percentile: Largest Contentful Paint 2.68s, Interaction to Next Paint 352ms, and Cumulative Layout Shift 0.17, all flagged orange or red on the score bar.
Joan León 🏞️⚡️ retweeted
⚡Featured posts this week:
✨ Submit your proposals for Interop 2027: @rachelandrew
✨ Reading a performance profile: @nucliweb
✨ HTML over WebSockets: @androsfenollosa
✨ Intro to Web UX and Speed Optimization: @sergeyche
🙏 Special thanks to the authors!
#webperf
ALT WebPerformance Report performance email preview highlighting optimization scores, Perf Links, and Core Web Vitals metrics on a colorful gradient background.
Joan León 🏞️⚡️ retweeted
Here's what's new in Modern Web Guidance v0.0.186 → goo.gle/4xcsdWW
⌨️ New guide on IME-safe textarea submission, along with recs for handling KeyboardEvent.isComposing for IME
🔎 Mandatory code verification step for agents in the global MWG skill