iiinova — where your digital self keeps evolving

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Ben Schwarz @benschwarz.bsky.social · 29/09/2026

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

calibreapp.com

Lazy Loading Images and Media: How Far Ahead Browsers Fetch

How far ahead Chrome, Firefox and Safari fetch lazy media, why a lazy hero image slows your page, and where to use lazy, eager and fetchpriority.

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Ryan Townsend @twnsnd.com · 28/09/2026

So happy to share mine & @nicj.net's first @cloudflare.social blog post—during our 16th Birthday Week no less! 🥳 Today we announce BEACON, a #webperf research dataset we're contributing to the @rumarchive.com community. blog.cloudflare.com/how-fast-is-...

blog.cloudflare.com

How fast is the web? Explore billions of real-user measurements with BEACON

Cloudflare is open-sourcing the BEACON dataset, making billions of anonymized Real User Monitoring (RUM) performance records publicly available on Google BigQuery.

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Joan León @nucliweb.net · 20/09/2026

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

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.

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Joan León @nucliweb.net · 07/09/2026

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.

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Thomas Steiner @tomayac.com · 28/08/2026

🤩 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...).

joanleon.dev

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...

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WebPerformance Report @webperfreport.bsky.social · 21/08/2026

Five reports. Five dimensions. One place. ✨ We’re just a few days away from launching our new Google Search Console Report. With SEO, our 360° reporting vision now covers: ⚡ Performance 🔐 Security ♿ Accessibility 📊 Analytics 🔎 SEO Coming soon. 🚀 #webperf #SEO #UX

WebPerformance Report dashboard showing the new report creation dialog with five report types: WebPageTest for performance, HTTP Observatory for security, WAVE for accessibility, GA4 for analytics, and the upcoming Google Search Console report for SEO.

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Joan León @nucliweb.net · 11/08/2026

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

joanleon.dev

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.

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Joan León @nucliweb.net · 13/08/2026

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

joanleon.dev

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...

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Martin Michalek @machal.bsky.social · 14/08/2026

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

perf.reviews

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.

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Andy Davies @andydavies.me · 12/08/2026

This is an excellent explanation of the lag that exists in CrUX data Recently had a customer who made huge improvements to INP but it took nearly four weeks for it to show in CrUX

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Joan León @nucliweb.net · 24/07/2026

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

perf.reviews

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.

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Joan León @nucliweb.net · 19/07/2026

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.

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Joan León @nucliweb.net · 28/05/2026

“Most teams fall into a reactive performance decay cycle: ship, wait for complaints, panic, patch, repeat. The Fast by Default model provides a repeatable alternative that keeps systems healthy.” Performance Engineering in Practice, by @denodell.bsky.social #WebPerf #Performance

Slide titled “1.6 Summary” from a presentation called “Performance Engineering in Practice.” The slide contains bullet points about software performance engineering. A highlighted bullet states that many teams fall into a reactive performance decay cycle: they ship software, wait for complaints, panic, patch issues, and repeat the cycle. It adds that the “Fast by Default” model offers a repeatable alternative that keeps systems healthy. The slide has a light gray background with dark blue and black text, and the page number “74” appears at the bottom center.

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Joan León @nucliweb.net · 28/05/2026

Llevo tiempo viendo demos de multiagentes y casi todas sufren de lo mismo: un agente escribe y otro revisa... para acabar haciendo una todo-app No son malas demos, pero no hay un motivo técnico real para dividirlas en agentes. Así no aprendemos cuándo sí tiene sentido Hilo con una alternativa 👇

Diagrama del flujo de un servidor MCP llamado ‘image-optim-mcp’ para optimización de imágenes. A la izquierda aparece una imagen de paisaje que entra al servidor. En el centro se muestra la configuración del servidor (nombre, versión, protocolo y herramientas: analyze, encode, judge y batch). A la derecha se comparan formatos de salida y reducción de tamaño: mozJPEG (-62 %, calidad 92,1), WebP (-68 %, 94,3), AVIF (-72 %, 95,2) y JPEG XL (-75 %, 95,6). Un panel final resume métricas: calidad perceptual SSIMULACRA2 de 95,6/100, reducción de peso del 75 % y latencia 4 veces más rápida.

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Joan León @nucliweb.net · 14/05/2026

Safari and Firefox change how big sites render based on the domain. TikTok, Netflix, Instagram… even SeatGuru. Chrome doesn’t. Why is that? denodell.com/blog/browser... by @denodell.bsky.social #Browser

denodell.com

Browsers Treat Big Sites Differently

Safari and Firefox change how big sites render based on the domain. TikTok, Netflix, Instagram… even SeatGuru. Chrome doesn’t. Why is that?

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Joan León @nucliweb.net · 13/05/2026

¿Buscas optimizar el rendimiento de tus aplicaciones con agentes de IA? En este workshop aprenderás a conectar el Chrome DevTools MCP a un agente para automatizar la detección de problemas. Veremos cómo generar reportes técnicos, de cliente y de management 👇 ¡Inscríbete aquí! #WebPerf #AI #MCP

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PerfReviews @perf.reviews · 07/05/2026

Running performance audits by hand, scripts in DevTools, results scattered, is fine until you're doing it on every project I built PerfReviews Insights to skip that. URL in, structured report out. Fonts, images, CSS, LCP, TTFB. Pro accounts keep full history perf.reviews/insights #WebPerf

perf.reviews

PerfReviews Insights — Web Performance Analyzer

Analyze any website and get an instant performance report: images, videos, third-party scripts, and page weight.

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Joan León @nucliweb.net · 06/05/2026

El agente de IA no sabe debuggear rendimiento si tú no le das el contexto para hacerlo. No es que sea malo. Por defecto trabaja a ciegas: sin acceso al navegador, sin trazas reales. #WebPerf #Performance #AIAgents #ChromeDevTools #Frontend

Banner promocional de un workshop titulado “Web Performance Debugging with AI Agents + Chrome DevTools MCP”. La imagen muestra una interfaz futurista con gráficos de rendimiento web, líneas de tiempo y métricas como LCP, INP y CLS conectadas a bloques etiquetados “MCP”, “API” y “AI”. A la derecha aparecen fragmentos de código y elementos visuales de análisis técnico sobre un fondo oscuro con tonos azules y verdes.

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Joan León @nucliweb.net · 29/04/2026

I've finished the #WebGPU in the browser series. 4 articles: fundamentals, image processing, real-time ML, and video editing Never written a shader before starting. In the last article we process video at 2ms per frame with WebGPU + WebCodecs joanleon.dev/en/webgpu-br... #WebPerf #JavaScript

joanleon.dev

WebGPU: the browser's new performance engine | Joan León

WebGPU exposes the GPU directly to the browser, opening new possibilities for intensive processing: images, video, ML, and more.

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Joan León @nucliweb.net · 27/04/2026

Toggle CSS classes in bulk, then reset the scroll: two lines that force the browser to block the main thread synchronously. I documented how to detect it in the Performance Panel and why one requestAnimationFrame is not enough to fix it. #WebPerf #CSS #DevTools #JavaScript

Screenshot of Chrome DevTools Performance panel analyzing a “Forced Synchronous Layout” demo running on localhost. The interface shows a timeline with CPU activity, animations, and style recalculations highlighted. A checkbox labeled “Enable CSS selector stats (slow)” is turned on in the top-right settings. A large red annotation circle and arrow emphasize the “Selector stats” section at the bottom, which lists CSS selectors, elapsed time, match counts, and performance impact. On the left side of the page, a scrollable list of text items (quotes from The Matrix) is visible, representing the app being profiled.

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mattzeunert.com @mattzeunert.com · 22/04/2026

The DebugBear custom dashboards feature is live now! We provide a flexible interface where you can display the web performance data that matters to your team. youtu.be/96fFkixiC8Y

youtu.be

How to create custom web performance dashboards for your team

YouTube video by DebugBear

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Joan León @nucliweb.net · 21/04/2026

Thanks to Codemotion for giving me the opportunity to continue sharing my knowledge on #WebPerf (aka improving the UX), and to do so in a workshop format where we use Chrome DevTools MCP to identify performance issues on a website with AI agents. #WebPerf #PerfTools #DevTools #CodemotionMadrid

Joan León stands at the front of a classroom giving a presentation to a small group of seated attendees. He gestures while speaking beside a large screen displaying slides about web performance. The audience, some using laptops, face him attentively in a modern, well-lit room with large windows.

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Joan León @nucliweb.net · 16/04/2026

A Gaussian blur in Canvas 2D takes 280ms. The same filter with WebGPU: 8ms. I wrote the second article in the WebGPU series: image processing in the browser with WGSL shaders and real benchmarks. joanleon.dev/en/webgpu-im... #WebPerf #WebGPU #JavaScript #Performance

joanleon.dev

Image processing in the browser with WebGPU | Joan León

How to use WebGPU to apply filters and transformations to images in the browser. Real benchmarks comparing with Canvas 2D.

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Joan León @nucliweb.net · 16/04/2026

I wrote about the experimental chrome-devtools-mcp CLI: a persistent daemon and direct subcommands to control Chrome from the terminal without writing code. Network, performance, Lighthouse, memory, interactions. All from the shell. joanleon.dev/en/chrome-de... #WebPerf #DevTools #JavaScript

joanleon.dev

Automate the browser from the terminal with Chrome DevTools MCP CLI | Joan León

The chrome-devtools-mcp package includes an experimental CLI that lets you control Chrome directly from the terminal: navigate, interact, audit performance, analyze network and memory, all without lea...

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Joan León @nucliweb.net · 09/04/2026

Just published the first article of a series. Covers what WebGPU is, CPU vs GPU for performance, and when to use it (vs WebAssembly). Next: image processing, ML inference, and real-time video, with real code and benchmarks. 👉 joanleon.dev/en/webgpu-br... #WebPerformance #WebGPU #JavaScript

joanleon.dev

WebGPU: the browser's new performance engine | Joan León

WebGPU exposes the GPU directly to the browser, opening new possibilities for intensive processing: images, video, ML, and more.

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Joan León @nucliweb.net · 12/04/2026

Sometimes opportunities come along that push you out of your comfort zone. An international product, millions of visits, and impact at scale. Definitely an exciting challenge. #WebPerf #CoreWebVitals #PerfChallenge

Screenshot of a Core Web Vitals report for a webpage on mobile devices dated April 4, 2026. It shows “Loading Performance is poor and stable,” “Interactivity is good but regressing,” and “Visual Stability is poor and stable.” A line chart displays trends over time for three metrics: Largest Contentful Paint (LCP) in red remaining high (around 5.2 seconds), Interaction to Next Paint (INP) in green staying low (around 182 ms), and Cumulative Layout Shift (CLS) in red remaining high (around 0.79). A tooltip highlights data from late September to late October 2025. On the right, definitions explain that good thresholds are LCP under 2.5 seconds, INP under 200 ms, and CLS under 0.1.

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Joan León @nucliweb.net · 01/04/2026

Software is evolving fast. My focus hasn’t changed: helping teams improve performance, UX, and conversion AI generates working code faster than ever… but not optimized for performance That’s where we add value: from “it works” to “it’s excellent” Reading @addyosmani.bsky.social’s new book

A copy of “Web Performance Engineering in the Age of AI” by Addy Osmani placed on a light wooden surface, showing the cover with a greyhound illustration and a clean, minimalist design.

An open book showing Chapter 3 titled “AI-Generated Code and the Performance Paradox,” with printed text discussing how AI-generated code can be functional but not always optimized for performance.

An open book showing Chapter 12 titled “Web Performance Case Studies and Success Stories,” with text describing real-world examples of performance optimization and business impact.

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Joan León @nucliweb.net · 28/03/2026

WebPerformance Report is no longer just a weekly report in your inbox Well done, @webperfreport.bsky.social team #WebPerf #Accessibility #Performance #Security #WebPerfReport

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Joan León @nucliweb.net · 27/03/2026

A measurement that varies with the model's interpretation is not a measurement. It's an estimate. I've written about separating deterministic measurement from AI analysis in web performance audits. #WebPerf #Performance #PerfReview #AI #DevTools

The complete audit workflow#
With Claude Code or Gemini, Chrome DevTools MCP, and the WebPerf SKILLs installed, the complete audit workflow goes from a series of scattered manual actions to a process the agent runs end to end:

1. Navigate to the URL (navigate_page)
2. Measure Core Web Vitals → run LCP.js, CLS.js, INP.js
3. If LCP > threshold → run LCP-Sub-Parts.js
4. If TTFB > threshold → run TTFB-Sub-Parts.js
5. Analyze resources → run Render-Blocking.js, Preload-Async-Conflicts.js
6. Collect all JSON results
7. Generate report with diagnosis, prioritization, and concrete solutions
8. Export in the required format (markdown, PDF, Slack)

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PerfReviews @perf.reviews · 18/03/2026

React SSR Framework Showdown: TanStack Start, React Router, and Next.js Under Load blog.platformatic.dev/react-ssr-fr... by @nodeland.dev #React #Performance

blog.platformatic.dev

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PerfReviews @perf.reviews · 14/03/2026

🚀 PerfReviews Insights: two new metrics to audit your web performance We've added two new analyses to the tool: #WebPerf #Performance #PerfReviews #WebPerfInsights

Screenshot of the PerfReviews Insights dashboard analyzing joanleon.dev with the “LCP” (Largest Contentful Paint) metric selected. The LCP value is 0.88 seconds, marked Good. The interface identifies the LCP element as a text paragraph with selector .astro-j7pv25f6 and size 40,592 px². The sidebar shows other performance checks including TTFB, images, videos, page weight, and external scripts.

Screenshot of the PerfReviews Insights dashboard analyzing the website joanleon.dev on a mobile viewport (390×844, iPhone 14). The “TTFB” (Time to First Byte) metric is selected in the sidebar. The result shows a TTFB of 203 ms, labeled Good. A connection breakdown chart shows DNS lookup (15 ms, 4%), TCP connect (161 ms, 45%), TLS handshake (158 ms, 44%), and server request (25 ms, 7%). The page includes explanations of the TTFB metric and links to optimization resources.

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Joan León @nucliweb.net · 10/03/2026

Muchas webs siguen sirviendo imágenes PNG de 2–3 MB. Pero esas mismas imágenes pueden pesar menos de 50 kB. La optimización de imágenes sigue siendo uno de los mayores problemas de rendimiento en la web. Hilo 👇

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Joan León @nucliweb.net · 13/03/2026

Chrome is bringing AI directly into the browser with the Summarizer API. In this post I show how to add an AI-generated summary to blog posts using the Chrome Summarizer API and models running locally in the browser. No external APIs. No token costs. #AI #WebAI #JavaScript #Chrome

Screenshot of a blog post on Joan León’s website titled “Adding an AI summary to blog posts with the Chrome Summarizer API.” The page shows a button labeled “AI Summary” and a highlighted summary box containing bullet points that explain how the Chrome Summarizer API works, including local summarization with Gemini Nano, browser requirements, streaming summaries, and implementation details. The site navigation and language selector are visible at the top.

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PerfReviews @perf.reviews · 11/03/2026

I built a free tool to analyze web performance: no login, no setup. Paste a URL → get an instant report on images, videos, page weight and third-party scripts. It's in beta. Try it 👇 #WebPerf #Performance #PerfInsights

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Chrome for Developers @developer.chrome.com · 09/03/2026

Starting with Chrome 145, DevTools now lets you throttle specific requests instead of the whole page. It’s the ideal way to test how your app handles a single slow asset or API call → goo.gle/4aP1Tcc

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PerfReviews @perf.reviews · 10/03/2026

Today I’d like to thank Leboncoin for the opportunity to collaborate with their team over the past few weeks. It was a pleasure to analyze their platform, work on improving observability, and share methodologies to identify and prioritize Web Performance optimization opportunities.

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Joan León @nucliweb.net · 08/03/2026

WebPerf Snippets agent-first WebPerf Snippets SKILLs were written for humans: emojis, colours, tables. The agent had to parse all of that. I added structured JSON returns and a build with terser that removes the console code. 80 lines → ~300 characters. #WebPerf #AI #Performance

Stylized screenshot of a dark code editor window titled “WebPerf Snippets agent-first: structured returns and minimal tokens.” It contrasts two approaches:
• Before: an agent parsing a console string like “🟢 LCP: 1.24s (good)”.
• After: a structured JSON-like object containing performance data for the Largest Contentful Paint (LCP) metric, including fields such as script: "LCP", status: "ok", metric: "LCP", value: 1240, unit: "ms", rating: "good", thresholds for good and needs improvement, and details about the measured element (img.hero, hero.avif, sizePixels: 756000).

The graphic illustrates the shift from parsing human-readable console output to returning structured performance data for agents.

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Web Standards @web-standards.dev · 26/02/2026

Practical guide to the <img> element: from basics to LCP. @nucliweb.net shows how srcset, sizes, modern formats AVIF and WebP via <picture>, fetchpriority, preload for the LCP image, and CDNs can improve Core Web Vitals. #performance #html joanleon.dev/en/guia-prac...

“Practical guide to the img element: from the basics to LCP” title, author’s name Joan León, code snippets, table of contents, and hashtags: images, webperf, core-web-vitals, html.

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Joan León @nucliweb.net · 06/03/2026

The JPEG XL Image Coding System History, Features, Coding Tools, Design Rationale, and Future arxiv.org/pdf/2506.05987 #Image #JpegXL

arxiv.org

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Joan León @nucliweb.net · 04/03/2026

I've been using WebPerf Snippets in my audits for years. Scripts to measure LCP, INP, CLS, TTFB, Render Blocking... The next step: turning them into tools an AI agent can use autonomously. But there's a design decision that makes all the difference. 🧵 #WebPerf #WebPerformance #AI #DevTools #MCP

WebPerf Snippets and Agent SKILLs: deterministic audits with Chrome DevTools MCP

Claude Code report showing Usercentrics scripts causing performance issues by combining 'preload' and 'async'. It recommends removing preloads or using fetchpriority='low' to avoid competing with critical LCP resources.

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Joan León @nucliweb.net · 20/02/2026

I've encountered many applications with poor INP due to long tasks that do not yield control to the browser I've written a guide with measurable examples comparing setTimeout, queueMicrotask, scheduler.postTask. It includes snippets to audit your projects joanleon.dev/en/yield-to-... #WebPerf

joanleon.dev

Yield to Main: setTimeout vs queueMicrotask vs scheduler.postTask | Joan León

A practical guide on how to use setTimeout, queueMicrotask and scheduler.postTask to break up long tasks and optimize INP. Comparison with measurable examples.

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Joan León @nucliweb.net · 23/02/2026

Last week I delivered a Web Performance training for part of the Basetis technical team: 2 days of theory and hands-on practice with real cases. We covered Core Web Vitals, RUM & Lab monitoring, Chrome DevTools, Lighthouse CI, Playwright and more... at the iconic La Pedrera. #WebPerf #Training

Joan Leon delivering a Web Performance training session to a group of professionals, pointing at a large screen displaying web development tools while attendees listen seated in a training room.

Detail of La Pedrera’s façade featuring its distinctive wrought iron balconies and wavy stone shapes, seen from street level and from a balcony overlooking the avenue.

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