Joan León
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nucliweb.net
Joan León
@nucliweb.net
1.8K followers 470 following 500 posts
⚡️ Web Performance Artisan at @perf.reviews | Google Dev Expert in Web Tech | Cloudinary Ambassador | ❤️ Image Optimization | Girona
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nucliweb.net
December 2025 dataset is now available & it covers 17,288,655 origins, a decrease of 6.5% over last month

67.6% of origins (↓ 0.5%) had good LCP
80.3% of origins (↑ 0.1%) had good CLS
85.6% of origins (↓ 0.6%) had good INP
54.4% of origins (↓ 0.4%) had good LCP, CLS and INP

#CoreWebVitals #WebPerf
January 13, 2026 at 9:40 PM
Reposted by Joan León
paul.irish
Been loving NVIDIA's NeMo models recently to complement Whisper for transcription, but the startup felt a bit heavy.

So I went on a profiling adventure!
github.com/NVIDIA-NeMo/...

Turned out to be fruitful… stoked to land a big optimization in NeMO.
github.com/NVIDIA-NeMo/...
A flame chart of loading NVIDIA's flagship ASR model, Canary. Captured with viztracer and shown in trace.cafe. It shows the load takes 52 seconds only for 3s of inference! Several annotations point out some opportunities for optimization (redundant tar extract, config read/write thrashing etc)
January 10, 2026 at 10:10 PM
nucliweb.net
I’ve decided to invest time in learning WebAssembly with the aim of improving the performance of some products

I know that WebAssembly isn’t a silver bullet that solves everything, but there are use cases where it can significantly improve a product’s UX

#WebPerf #WebAssembly #Performance
Four books about WebAssembly and Rust laid out in a 2×2 grid on a gray fabric surface. The covers include titles such as Accelerating the DOM with WebAssembly, WebAssembly Unleashed with Rust & Go, Rust WebAssembly, and Rust for WebAssembly, featuring modern, tech-themed designs focused on high-performance web development.
January 8, 2026 at 3:08 PM
Reposted by Joan León
debugbear.com
Did you know you can add annotations to your web performance charts on DebugBear?

www.debugbear.com/docs/annotat...
January 7, 2026 at 3:38 PM
Reposted by Joan León
web-standards.dev
Debugging web performance with Chrome DevTools. @nucliweb.net shows how to triage big assets in Network, read CrUX live Core Web Vitals, and use Performance Insights and traces to improve LCP, CLS, and INP. #performance #devtools #chrome

calendar.perfplanet.com/2025/chrome-...
Chrome DevTools for debugging web performance.
January 7, 2026 at 12:00 PM
Reposted by Joan León
perf.reviews
When web performance degrades, the impact is immediate.

Conversions drop. UX suffers. SEO follows.

The problem? These issues are often detected too late.
Side-by-side screenshot showing a WebPerformance Report email with Core Web Vitals metrics and a highlighted “Need Expert Guidance?” call-to-action on the left, and a web form titled “Request Expert Guidance from our Technical Partners” on the right, where users can enter contact details and select technical partners (Digital Loop or PerfReviews).
January 5, 2026 at 9:36 AM
nucliweb.net
A Visual Guide to Fundamentals by @sarahedo.bsky.social

www.youtube.com/watch?v=tGnv...
Keynote: A Visual Guide to Fundamentals - Sarah Drasner
YouTube video by OpenJS Foundation
www.youtube.com
January 5, 2026 at 3:45 PM
Reposted by Joan León
mattzeunert.com
Wrote a bit more about the memory leak we fixed recently, and why we ignored it for 6 years.

Thanks to @nucliweb.net for sharing some of his questions!

www.debugbear.com/blog/javascr...
We Fixed A 6-Year-Old JavaScript Memory Leak | DebugBear
How we discovered and fixed a lodash memoize memory leak that caused out of memory crashes in our Google Cloud Functions.
www.debugbear.com
January 5, 2026 at 1:10 PM
Reposted by Joan León
stoyan.me
New blog post: www.phpied.com/maximally-mi...
It's about staying away from most everything the JS ecosystem has to offer and stick close to the web platform. A build is still necessary because of long lived caches and updates but it can be tiny and simple. Time will tell how this strategy plays out
Maximally Minimal Build Process
In my previous post I described how I set up sightread.org with no build process and modern JavaScript. The goal was raw ES modules, no transpilation, no bundling, just <script type="module"> and we'r...
www.phpied.com
January 4, 2026 at 11:09 PM
Reposted by Joan León
infrequently.org
New year, new web performance mystery (and it's a huge one):

calendar.perfplanet.com/2025/the-cur...
December 31, 2025 at 8:29 PM
nucliweb.net
📣 Nuevo post: Chrome DevTools para depurar el rendimiento de una web

Una guía paso a paso de cómo utilizo Chrome DevTools para detectar problemas de Web Performance en una web, así como validar algunas hipótesis

joanleon.dev/posts/chrome...

#WebPerf #DevTools
Chrome DevTools para depurar el rendimiento de una web | Joan León
Una guía paso a paso de cómo utilizo Google Chrome DevTools para detectar problemas de Web Performance en una web, y validar algunas hipótesis para solventarlos.
joanleon.dev
January 2, 2026 at 11:58 AM
nucliweb.net
🚀 WebPerf Snippets – Major Update

✨ What’s new
• Visual ratings 🟢/🟡/🔴
• Clean tables report
• Automatic summaries
• Issue detection with actionable recommendations
• Improved docs with causes, fixes & official links

👉 webperf-snippets.nucliweb.net

#WebPerf #CoreWebVitals #JavaScript #DevTools
WebPerf Snippets | WebPerf Snippets
A curated list of snippets to get Web Performance metrics to use in the browser console or as snippets on Chrome DevTools by Joan León
webperf-snippets.nucliweb.net
January 2, 2026 at 7:56 AM
nucliweb.net
I’m starting the year by migrating the webperf-snippets.nucliweb.net project to the latest versions.

I’m also improving the documentation and scripts, with better console output.

Keep an eye out for upcoming updates

#WebPerf #WebPerfSnippets #PerfTools #Performance #DevTools
January 1, 2026 at 10:48 AM
nucliweb.net
Marketing: Hello, Joan! Can we add a short video as a background in the hero component?

Me: 🫠

#WebPerf #Performance #TrueStories
Screenshot of a macOS file information window. Red boxes highlight the file size (274.5 MB) and the video metadata, which includes a resolution of 3840x2160, HEVC codecs, and a duration of 8 seconds.
December 30, 2025 at 6:50 PM
Reposted by Joan León
sergeyche.dev
Our Web Performance Journey guide is live on PerfPlanet Calendar!
stoyan.me Stoyan Stefanov @stoyan.me · 15d
Web Performance Calendar day 30 with @sergeyche.dev, Eric Goldstein and Alex Chernyshev on mastering perf: get business to care, link UX speed to outcomes, set thresholds, understand real users with percentiles, trends, distributions, tie to business metrics
calendar.perfplanet.com/2025/7-steps...
7 Steps of a Web Performance Journey
This year, Sergey Chernyshev, Eric Goldstein, and Alex Chernyshev - members of the NY Web Performance meetup - decided to collaborate on the future of the UX Speed Calculator tool Sergey created a few...
calendar.perfplanet.com
December 30, 2025 at 4:41 PM
Reposted by Joan León
stoyan.me
Web Performance Calendar day 28 when Ian Duffy shows us how to tame Chrome’s Performance panel: reduce noise, search fast, annotate, use Insights, and customize tracks

calendar.perfplanet.com/2025/tips-fo...
Tips for making the Performance Panel less overwhelming
Introduction The Performance Panel is used for detailed investigations on traces captured during page load or during user interactions. It's a critical tool for understanding and debugging performanc...
calendar.perfplanet.com
December 28, 2025 at 4:40 PM
Reposted by Joan León
stoyan.me
Web Performance Calendar day 27 with @nucliweb.net on using Chrome DevTools for fun and profit: inspect heavy files in Network panel, monitor Core Web Vitals, record performance traces, validate optimizations, and more.

calendar.perfplanet.com/2025/chrome-...
Chrome DevTools for Debugging Web Performance
This is a step-by-step guide on how I use Chrome DevTools (DevTools from now on) to detect Web Performance issues on a website, as well as validate hypotheses to fix some of the problems found. Discl...
calendar.perfplanet.com
December 27, 2025 at 2:47 PM
nucliweb.net
La propiedad CSS content-visibility puede mejorar significativamente el rendimiento de renderizado, especialmente en páginas con mucho contenido

En este post: cómo funciona, un caso real con métricas antes/después, y snippets para auditar

joanleon.dev/posts/conten...

#WebPerf #Performance #CSS
Optimiza el renderizado con content-visibility | Joan León
La propiedad CSS content-visibility mejora el rendimiento de renderizado. Caso práctico con métricas y snippets para detectar oportunidades.
joanleon.dev
December 27, 2025 at 11:25 AM
nucliweb.net
How to load CSS (fast)

calendar.perfplanet.com/2025/how-to-... by @yoavweiss

#WebPerf #CSSPerf #Performance #CSS
How to load CSS (fast)
Loading styles on the web is something that looks trivial at first. You just add a <link rel=stylesheet> to your page (or <style> for inline styles) and you're done. But if you wanted to load CSS fas...
calendar.perfplanet.com
December 22, 2025 at 9:01 AM
Reposted by Joan León
stoyan.me
Web Performance Calendar day 21 with Conor McCarthy and lessons learned from web perf client site reviews

calendar.perfplanet.com/2025/insight...
Insights from 100 site speed reviews in 2025
Over the course of 2025, I have completed 100 site speed reviews at DebugBear. This is a free service we offer to trial accounts looking for a brief assessment of their current web performance. Reque...
calendar.perfplanet.com
December 21, 2025 at 11:27 AM
nucliweb.net
Why Your Server Is Paying for Your CSS Choices

dp-lewis.medium.com/why-your-ser...

#CSS #WebPerf #ServerPerf
Why Your Server Is Paying for Your CSS Choices
Server-side rendering makes some previously invisible costs very visible. This post explores how styling can end up on the server’s hot…
dp-lewis.medium.com
December 21, 2025 at 9:56 AM
Reposted by Joan León
jensimmons.bsky.social
Check out all the revised demos of Grid Lanes in Safari Technology Preview 234!

webkit.org/demos/grid3/
CSS Grid Lanes is now in Safari Technology Preview 234.
December 20, 2025 at 1:31 AM
nucliweb.net
Updated de Content-Visibility snippet for Chrome DevTools

- Detects existing content-visibility usage
- Finds offscreen optimization opportunities
- CLS warnings for missing contain-intrinsic-size
- Configurable thresholds

webperf-snippets.nucliweb.net/Loading/Cont...

#WebPerf #PerfTools
Content Visibility – Nextra
A curated list of snippets to get Web Performance metrics to use in the browser console or as snippets on Chrome DevTools by Joan León
webperf-snippets.nucliweb.net
December 20, 2025 at 12:41 AM
nucliweb.net
About to start a new Web Performance consulting project & I’m really looking forward to it

I’m sure I’ll enjoy working on this, and the impact on the client’s conversions should be very noticeable 📈

Performance is where UX and business truly meet

#WebPerf #WebPerformance #CoreWebVitals #UX
Screenshot of Google Search Console Core Web Vitals report for a URL on mobile (as of Dec 12, 2025). Overall status shows Loading Performance: poor, Interactivity: poor, and Visual Stability: needs improvement, all stable. A timeline chart displays red trends for LCP and INP and a yellow trend for CLS. Tooltip indicates data from Nov 15–Dec 12, 2025: 75% of phone Chrome page loads have LCP 9,035 ms, INP 1,031 ms, and CLS 0.11. Buttons labeled “Explore Loading Performance” and “Explore Visual Stability” appear on the right.
December 19, 2025 at 4:50 PM
Reposted by Joan León
stoyan.me
Web Performance Calendar day 19 with Alex Podelko on how performance engineering has evolved with computing: from mainframes to distributed systems, web/mobile, cloud, AI. Knowing your history may help reduce wheel-reinvention and encourage skills reuse

calendar.perfplanet.com/2025/a-short...
A Short History of Performance Engineering
A long time ago, in 2014, I did the “A Short History of Performance Engineering” Ignite talk at the Velocity conference (slides and video). A lot of new developments have happened since 2014, so here ...
calendar.perfplanet.com
December 19, 2025 at 8:34 AM