Joan León
@nucliweb.net
⚡️ Web Performance Artisan at @perf.reviews | Google Dev Expert in Web Tech | Cloudinary Ambassador | ❤️ Image Optimization | Girona
Reposted by Joan León
How do you measure when a component is “ready”? ⏱️
LCP is too global; Element Timing is too specific.
🛠️ I’ve been working with Bloomberg on a new #webperf API: Container Timing. Think of it as “LCP for a web component”, providing aggregated paint timing for a subtree.
LCP is too global; Element Timing is too specific.
🛠️ I’ve been working with Bloomberg on a new #webperf API: Container Timing. Think of it as “LCP for a web component”, providing aggregated paint timing for a subtree.
February 10, 2026 at 4:06 PM
How do you measure when a component is “ready”? ⏱️
LCP is too global; Element Timing is too specific.
🛠️ I’ve been working with Bloomberg on a new #webperf API: Container Timing. Think of it as “LCP for a web component”, providing aggregated paint timing for a subtree.
LCP is too global; Element Timing is too specific.
🛠️ I’ve been working with Bloomberg on a new #webperf API: Container Timing. Think of it as “LCP for a web component”, providing aggregated paint timing for a subtree.
🚀 New WebPerf Snippet published!
Detects preload resource hints for scripts that use async or defer attributes. This is an anti-pattern that wastes bandwidth & can hurt performance by artificially elevating the priority of resources that should load at lower priority
#WebPerf #WebPerfSnippet
Detects preload resource hints for scripts that use async or defer attributes. This is an anti-pattern that wastes bandwidth & can hurt performance by artificially elevating the priority of resources that should load at lower priority
#WebPerf #WebPerfSnippet
February 11, 2026 at 3:27 PM
🚀 New WebPerf Snippet published!
Detects preload resource hints for scripts that use async or defer attributes. This is an anti-pattern that wastes bandwidth & can hurt performance by artificially elevating the priority of resources that should load at lower priority
#WebPerf #WebPerfSnippet
Detects preload resource hints for scripts that use async or defer attributes. This is an anti-pattern that wastes bandwidth & can hurt performance by artificially elevating the priority of resources that should load at lower priority
#WebPerf #WebPerfSnippet
Integrate CrUX data into performance trace summaries in Chrome DevTools MCP v0.17.0 👏
github.com/ChromeDevToo...
#WebPerf #PerfTools #DevTools
github.com/ChromeDevToo...
#WebPerf #PerfTools #DevTools
Release chrome-devtools-mcp: v0.17.0 · ChromeDevTools/chrome-devtools-mcp
0.17.0 (2026-02-10)
🎉 Features
include Error.cause chain for uncaught errors and logged Errors (#906) (05b01ec)
Integrate CrUX data into performance trace summaries (#733) (b747f9d)
show message a...
github.com
February 11, 2026 at 2:30 PM
Integrate CrUX data into performance trace summaries in Chrome DevTools MCP v0.17.0 👏
github.com/ChromeDevToo...
#WebPerf #PerfTools #DevTools
github.com/ChromeDevToo...
#WebPerf #PerfTools #DevTools
Reposted by Joan León
We recently added support for adding specific URLs to our CrUX trends dashboard – not just entire domains!
www.debugbear.com/docs/crux-tr...
www.debugbear.com/docs/crux-tr...
February 10, 2026 at 3:55 PM
We recently added support for adding specific URLs to our CrUX trends dashboard – not just entire domains!
www.debugbear.com/docs/crux-tr...
www.debugbear.com/docs/crux-tr...
Reposted by Joan León
A shocking 8.5% of sites that use CDNs deliver some static content directly to end users via cloud storage! Many are not compressing or caching this content either. This comes at a significant performance cost. Details, examples and @httparchive.org stats here - paulcalvano.com/2026-02-09-s...
February 9, 2026 at 12:34 PM
A shocking 8.5% of sites that use CDNs deliver some static content directly to end users via cloud storage! Many are not compressing or caching this content either. This comes at a significant performance cost. Details, examples and @httparchive.org stats here - paulcalvano.com/2026-02-09-s...
Reposted by Joan León
Announcing The CSS Selection!
📰 www.projectwallace.com/the-css-sele...
📚 100,000 websites
⏱️ 100+ metrics
🔖 7 chapters
The biggest deep-dive ever into real-world use of CSS across the globe. Dive in and find out some hidden gems. Also, see how much of 'the new CSS' is actually used!
📰 www.projectwallace.com/the-css-sele...
📚 100,000 websites
⏱️ 100+ metrics
🔖 7 chapters
The biggest deep-dive ever into real-world use of CSS across the globe. Dive in and find out some hidden gems. Also, see how much of 'the new CSS' is actually used!
The CSS Selection - 2026 Edition - Project Wallace
The CSS Selection shows real-world CSS usage from over 100,000 websites and looks at the most important metrics.
www.projectwallace.com
February 6, 2026 at 10:08 AM
Announcing The CSS Selection!
📰 www.projectwallace.com/the-css-sele...
📚 100,000 websites
⏱️ 100+ metrics
🔖 7 chapters
The biggest deep-dive ever into real-world use of CSS across the globe. Dive in and find out some hidden gems. Also, see how much of 'the new CSS' is actually used!
📰 www.projectwallace.com/the-css-sele...
📚 100,000 websites
⏱️ 100+ metrics
🔖 7 chapters
The biggest deep-dive ever into real-world use of CSS across the globe. Dive in and find out some hidden gems. Also, see how much of 'the new CSS' is actually used!
Excited to share my latest contribution to the Web Performance Calendar 2025!
In this post, I dive into using Chrome DevTools for debugging web performance, with tips to help you speed up your sites and improve user experience.
#WebPerf #Performance #DevTools #PerfTools
In this post, I dive into using Chrome DevTools for debugging web performance, with tips to help you speed up your sites and improve user experience.
#WebPerf #Performance #DevTools #PerfTools
February 2, 2026 at 9:22 AM
Excited to share my latest contribution to the Web Performance Calendar 2025!
In this post, I dive into using Chrome DevTools for debugging web performance, with tips to help you speed up your sites and improve user experience.
#WebPerf #Performance #DevTools #PerfTools
In this post, I dive into using Chrome DevTools for debugging web performance, with tips to help you speed up your sites and improve user experience.
#WebPerf #Performance #DevTools #PerfTools
Reposted by Joan León
Here's your friendly reminder that CSS selectors are global and evaluated RTL, so if you have selectors that are very broad like `.container > div` you might be impacting performance in a measurable way 🙈
Before and after profile of server switching after some selector optimizations in @discord.com
Before and after profile of server switching after some selector optimizations in @discord.com
January 27, 2026 at 4:41 PM
Here's your friendly reminder that CSS selectors are global and evaluated RTL, so if you have selectors that are very broad like `.container > div` you might be impacting performance in a measurable way 🙈
Before and after profile of server switching after some selector optimizations in @discord.com
Before and after profile of server switching after some selector optimizations in @discord.com
chrome-devtools-mcp: v0.14.0
🎉 Features
🔹 add a skill for using chrome-devtools-mcp
🔹 include stack trace in 'get_console_message' tool
🔹 support device viewport and user agent emulation
🔹 support filePath for network request and response bodies
🔹 and more…
#WebPerf #Chrome #DevTools
🎉 Features
🔹 add a skill for using chrome-devtools-mcp
🔹 include stack trace in 'get_console_message' tool
🔹 support device viewport and user agent emulation
🔹 support filePath for network request and response bodies
🔹 and more…
#WebPerf #Chrome #DevTools
January 27, 2026 at 1:58 PM
Reposted by Joan León
✍️ Just finished another code drawing in my AI series, this one's about MCP in practice. Enjoy!
January 26, 2026 at 2:01 PM
✍️ Just finished another code drawing in my AI series, this one's about MCP in practice. Enjoy!
Reposted by Joan León
My talk at @henrihelvetica.bsky.social's SPDY meetup in Toronto is live: www.youtube.com/watch?v=xq2c.... It's pretty rough and unpolished, but I included some fun stories of the history of performance work in Chrome which you likely can't find anywhere else. Slides: docs.google.com/presentation...
How To Get Your Boss To Let You Work On Web Performance, by Rick Byers of Google.
YouTube video by Henri Helvetica
www.youtube.com
January 20, 2026 at 3:53 PM
My talk at @henrihelvetica.bsky.social's SPDY meetup in Toronto is live: www.youtube.com/watch?v=xq2c.... It's pretty rough and unpolished, but I included some fun stories of the history of performance work in Chrome which you likely can't find anywhere else. Slides: docs.google.com/presentation...
Reposted by Joan León
In Firefox 147, you no longer need heavy libraries to (de)compress brotli with JS - you can just use CompressionStream and DecompressionStream!
January 21, 2026 at 3:34 PM
In Firefox 147, you no longer need heavy libraries to (de)compress brotli with JS - you can just use CompressionStream and DecompressionStream!
January 19, 2026 at 2:07 PM
Reposted by Joan León
The 2025 Web Almanac by HTTP Archive has been officially released! 🚀
We would like to thank all of our contributors from around the globe who made this extensive report possible!
Check out the full report here: almanac.httparchive.org
We would like to thank all of our contributors from around the globe who made this extensive report possible!
Check out the full report here: almanac.httparchive.org
January 16, 2026 at 3:00 AM
The 2025 Web Almanac by HTTP Archive has been officially released! 🚀
We would like to thank all of our contributors from around the globe who made this extensive report possible!
Check out the full report here: almanac.httparchive.org
We would like to thank all of our contributors from around the globe who made this extensive report possible!
Check out the full report here: almanac.httparchive.org
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
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
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
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
Reposted by Joan León
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/...
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/...
January 10, 2026 at 10:10 PM
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/...
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/...
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
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
January 8, 2026 at 3:08 PM
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
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
Reposted by Joan León
Did you know you can add annotations to your web performance charts on DebugBear?
www.debugbear.com/docs/annotat...
www.debugbear.com/docs/annotat...
January 7, 2026 at 3:38 PM
Did you know you can add annotations to your web performance charts on DebugBear?
www.debugbear.com/docs/annotat...
www.debugbear.com/docs/annotat...
Reposted by Joan León
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-...
calendar.perfplanet.com/2025/chrome-...
January 7, 2026 at 12:00 PM
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-...
calendar.perfplanet.com/2025/chrome-...
Reposted by Joan León
When web performance degrades, the impact is immediate.
Conversions drop. UX suffers. SEO follows.
The problem? These issues are often detected too late.
Conversions drop. UX suffers. SEO follows.
The problem? These issues are often detected too late.
January 5, 2026 at 9:36 AM
When web performance degrades, the impact is immediate.
Conversions drop. UX suffers. SEO follows.
The problem? These issues are often detected too late.
Conversions drop. UX suffers. SEO follows.
The problem? These issues are often detected too late.
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
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...
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
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...
Thanks to @nucliweb.net for sharing some of his questions!
www.debugbear.com/blog/javascr...
Reposted by Joan León
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
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
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
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
Reposted by Joan León
December 31, 2025 at 8:29 PM
📣 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
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
📣 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
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