Joan León
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nucliweb.net
Joan León
@nucliweb.net
1.9K followers 500 following 640 posts
⚡️ Web Performance Artisan at @perf.reviews | Google Dev Expert in Web Tech | Cloudinary Ambassador | ❤️ Image Optimization | Girona
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nucliweb.net
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
WebMCP on a static site: the GeeksCAT Conf 2026 website, ready for agents | Joan León
The GeeksCAT Conf 2026 website is a static Astro site that exposes its schedule, speakers and event details to AI agents through WebMCP. Three layers: a manifest in /.well-known, JSON endpoints genera...
joanleon.dev
September 16, 2026 at 6:32 PM
Reposted by Joan León
developer.chrome.com
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
September 16, 2026 at 6:30 PM
nucliweb.net
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
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. 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.
September 7, 2026 at 10:17 AM
Reposted by Joan León
webperfreport.bsky.social
⚡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
WebPerformance Report performance email preview highlighting optimization scores, Perf Links, and Core Web Vitals metrics on a colorful gradient background.
September 6, 2026 at 12:58 PM
Reposted by Joan León
tomayac.com
🤩 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...).
HTTP cache partitioning: the same image, downloaded twice | Joan León
A page with a cross-site iframe requests the same image from the iframe and from the parent. Chrome downloads it twice; Firefox and Safari, once. Why the cache key differs across the three engines, wh...
joanleon.dev
August 28, 2026 at 3:12 PM
Reposted by Joan León
webperfreport.bsky.social
⚡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
WebPerformance Report performance email preview highlighting optimization scores, Perf Links, and Core Web Vitals metrics on a colorful gradient background.
August 16, 2026 at 7:00 PM
nucliweb.net
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
A dark-themed presentation slide titled "TL;DR" displaying tips for optimizing Claude API usage and token efficiency. The slide is divided into two columns: Left column discusses: - Using `/clear` command between tasks to prevent context carryover and reduce token usage - Setting model and effort level before starting a session to avoid breaking the prompt cache mid-conversation - Mentioning files with @ notation instead of naming them, to attach files directly and save API calls Right column covers: - Adding quiet flags to commands or running them in a subagenr to manage noisy output while keeping results in the conversation - Running `/context` once per session to review loaded content (CLAUDE.md and MCP tool definitions) and remove unnecessary items - Running `/compact` before breaks, since prompt cache expires after an hour and summarizing conversations is cheaper while the cache is active
August 16, 2026 at 9:43 AM
Reposted by Joan León
machal.bsky.social
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
Reading a Performance Profile: Field Guide
An interactive field guide to the Chrome DevTools Performance panel: waterfall, flame chart, LCP, CLS, INP, and the Insights panel.
perf.reviews
August 14, 2026 at 6:10 AM
nucliweb.net
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
A skill that knows nothing: the architecture of Modern Web Guidance | Joan León
Modern Web Guidance doesn't keep the knowledge in the skill, it teaches the agent to retrieve it. Local semantic search with MiniLM and TensorFlow.js, guides with their own grader, and empirical calib...
joanleon.dev
August 13, 2026 at 4:38 PM
nucliweb.net
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
The CrUX 28-day rolling window | Joan León
How the CrUX 28-day rolling window actually works, what each source publishes, and why p75 takes so long to move even though the data is only two days old.
joanleon.dev
August 11, 2026 at 9:50 PM
nucliweb.net
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...
A printed thank-you letter from Addy Osmani on a dark background, hand-signed and dated 2026, next to its opened envelope postmarked San Francisco. Four stickers lie beside it: "Coder", "Computer Club", a Cmd+Z one reading "Just Undo It", and a perfume bottle reading "#perfmatters".
August 5, 2026 at 8:45 AM
nucliweb.net
Web performance is a marathon, not a sprint. Ship the fastest site today and in two weeks a third-party script, an unoptimised image or a CDN change will have quietly undone it.

Optimising without monitoring doesn't last. 🧵

#WebPerf #RUM #CoreWebVitals
August 3, 2026 at 9:38 PM
Reposted by Joan León
en.sitnik.es
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.
July 30, 2026 at 12:23 PM
Reposted by Joan León
webperfreport.bsky.social
⚡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
WebPerformance Report performance email preview highlighting optimization scores, Perf Links, and Core Web Vitals metrics on a colorful gradient background.
July 26, 2026 at 12:47 PM
Reposted by Joan León
43081j.com
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 🩵
e18e - Ecosystem Performance - Open Collective
The e18e community has the aim of improving performance of tooling and packages in the JavaScript ecosystem.
opencollective.com
July 19, 2026 at 1:23 PM
nucliweb.net
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
Reading a Performance Profile: Field Guide
An interactive field guide to the Chrome DevTools Performance panel: waterfall, flame chart, LCP, CLS, INP, and the Insights panel.
perf.reviews
July 24, 2026 at 8:46 PM
Reposted by Joan León
sergeyche.dev
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.
nucliweb.net Joan León @nucliweb.net · Jul 19
An occupational habit: I open DevTools on every site I visit, hunting for things to improve. On skills.addy.ie I caught a 301 on every internal click, a wasted round trip.

It was a trailing-slash mismatch. Wrote up the finding and the fix: joanleon.dev/en/trailing-...

#WebPerf #Astro #Netlify
Screenshot of a desktop web browser displaying the agent-skills website on the left and Chrome DevTools’ Network tab on the right. The webpage heading reads “How agent-skills compares” with explanatory text describing how agent-skills relates to Superpowers and Matt Pocock’s skills, along with a “TL;DR” summary card. The DevTools Network panel shows document requests, including several 301 Moved Permanently redirects (such as skills, getting-started, lifecycle, teach, and compare) followed by corresponding 200 OK responses for URLs ending with trailing slashes. The browser address bar displays skills.addy.ie/compare/, and the Network panel is configured with Preserve log and Disable cache enabled and No throttling selected.
July 19, 2026 at 1:47 PM
nucliweb.net
An occupational habit: I open DevTools on every site I visit, hunting for things to improve. On skills.addy.ie I caught a 301 on every internal click, a wasted round trip.

It was a trailing-slash mismatch. Wrote up the finding and the fix: joanleon.dev/en/trailing-...

#WebPerf #Astro #Netlify
Screenshot of a desktop web browser displaying the agent-skills website on the left and Chrome DevTools’ Network tab on the right. The webpage heading reads “How agent-skills compares” with explanatory text describing how agent-skills relates to Superpowers and Matt Pocock’s skills, along with a “TL;DR” summary card. The DevTools Network panel shows document requests, including several 301 Moved Permanently redirects (such as skills, getting-started, lifecycle, teach, and compare) followed by corresponding 200 OK responses for URLs ending with trailing slashes. The browser address bar displays skills.addy.ie/compare/, and the Network panel is configured with Preserve log and Disable cache enabled and No throttling selected.
July 19, 2026 at 9:22 AM
nucliweb.net
I'm testing the @debugbear.com MCP with Claude Code, and my first impression is that combining DebugBear's great tools with the power of AI Agents is awesome for creating executive and detailed technical reports...

#WebPerf #PerfTools #AI #WebPerfAI
July 17, 2026 at 6:18 PM
nucliweb.net
Modern UI Patterns, by @una.im at CSS Day 2026
www.youtube.com/watch?v=8FSL...

#CSS #UI
Modern UI Patterns - Una Kravets - CSS Day 2026
YouTube video by Web Conferences Amsterdam
www.youtube.com
June 30, 2026 at 10:28 PM
nucliweb.net
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
Antigravity Skills: advanced YAML frontmatter configuration | Joan León
The kind, model, temperature, max_turns and tools fields in SKILL.md frontmatter let you precisely control how each agent runs in Antigravity. A practical guide to the extended fields that Google hasn...
joanleon.dev
June 13, 2026 at 11:07 PM
nucliweb.net
Friend: Hey, Joan, can you give us a hand?

Me: Sure, send me the URL

DevTools: It takes nearly 3 seconds to load the WordPress plugins

Me: 🫠
June 7, 2026 at 3:17 PM
nucliweb.net
Este fin de semana he podido conocer a Edu, ver su Keynote en @commit-conf.com, y conversar con él, y tengo muy claro que quiero leer ese libro 📖
eferro.net Edu Ferro (eferro) 🇵🇸 @eferro.net · Jun 7
Llevo 25+ años construyendo equipos y veo el mismo patrón: al principio entregáis rápido, pero cada feature, integración y decisión va sumando peso. Hasta que casi toda la energía del equipo se va en sostener lo que ya existe.
June 7, 2026 at 12:38 PM
nucliweb.net
Gracias @commit-conf.com por darme la oportunidad de compartir con la comunidad

Estas son las slides de la charla slides.com/joanleon/pat...

#CommitConf #WebPerf
June 6, 2026 at 2:21 PM
Reposted by Joan León
webperfreport.bsky.social
⚡Featured posts this week:
✨ Zero Trust Implementation Guidelines: National Security Agency
✨The Website Specification: @joost.blog
✨Agent Skills: @addyosmani.bsky.social @oreilly.bsky.social
✨Lighthouse agentic browsing scoring: @developer.chrome.com
🙏 Special thanks to the authors!
#webperf
WebPerformance Report performance email preview highlighting optimization scores, Perf Links, and Core Web Vitals metrics on a colorful gradient background.
May 31, 2026 at 12:36 PM