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Reposted by Joan León

Barry Pollard @tunetheweb.com · 8d

Core Web Vitals mystery for ya:

Why does Google Search Console same my LCP is bad, but every example URL has good LCP?

I see developers asking: How can this happen? Is GSC wrong? (I'm willing to bet it is not!) What can you do about it?

This is admittedly confusing so let's dive in...

🧵 1/12

Screenshot of Core Web Vitals graph in Google Search Console, with the URLs greyed out. The Group LCP is 2.6 seconds and so the group is in amber and saying there is an issue as it's longer than the 2.5 seconds "good" threshold. Yet all the examples have green LCPs of 1.7 seconds, 2.4 seconds, 1.2 seconds...etc. which is confusing.

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Joan León @nucliweb.net · 10d

New Web Performance challenge, improve the INP and LCP of this Web App.

Interaction to Next Paint
🟥 920ms in desktop
🟥 1800ms in mobile

Largest Contentful Paint
🟩 2.33s in desktop
🟥 4.13s in mobile

#WebPerformance #CoreWebVitals #INP

4

Joan León @nucliweb.net · 17d

One List To Rule Them All

nerdy.dev/cascading-se...

#CSS

One List To Rule Them All · September 10, 2025

In the darkness may it bind us

nerdy.dev

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Reposted by Joan León

Thomas Steiner @tomayac.com · 23d

On the Chrome team, we've a cool new origin trial for you to try in your apps: the Proofreader API: developer.chrome.com/docs/ai/proo....

❌ tyop → ✅ typo

```js
await (await Proofreader.create({
expectedInputLanguages: ['en'],
})).proofread(
'Let us knwo how it foes',
);
```

#BuiltInAI #WebAI

The Proofreader API | AI on Chrome | Chrome for Developers

Improve your content readability and grammar with the Proofreader API.

developer.chrome.com

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Joan León @nucliweb.net · 22d

📣 New version

Perfetto v52.0

github.com/google/perfe...

#WebPerf #PerfTools

Release Perfetto v52.0 · google/perfetto

We’re excited to share some highlights from the Perfetto v52 release. 🌙 Dark mode support The Perfetto UI now features a dark mode with theme-aware colors! Dark mode can be enabled via"settings" i...

github.com

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Joan León @nucliweb.net · 24d

200+ Resources to Become a Great Engineering Leader in 2025

newsletter.eng-leadership.com/p/200-resour..., by @gregorojstersek.bsky.social

#Engineering

200+ Resources to Become a Great Engineering Leader in 2025

List of books, newsletters & articles, people and more!

newsletter.eng-leadership.com

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Joan León @nucliweb.net · 29d

A basic package to quickly check if your npm project is using malicious versions of npm packages

github.com/oegea/is-my-...

GitHub - oegea/is-my-code-pwned: A basic package to quickly check if your npm project is using malicious versions of npm packages

A basic package to quickly check if your npm project is using malicious versions of npm packages - oegea/is-my-code-pwned

github.com

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Joan León @nucliweb.net · Sep 9

#TIL You can sent multiple Server-Timing headers

Screenshot of HTTP response headers showing three Server-Timing entries: cfCacheStatus with value HIT, cfOrigin with duration 0 and cfEdge with duration 18, and cfExtPri with no value.

Joan León @nucliweb.net · Aug 25

github.com/calibreapp/i...

GitHub - calibreapp/image-actions: A Github Action that automatically compresses JPEGs, PNGs and WebPs in Pull Requests.

A Github Action that automatically compresses JPEGs, PNGs and WebPs in Pull Requests. - calibreapp/image-actions

github.com

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Joan León @nucliweb.net · Aug 25

#WebPerfTip

If you need a GitHub Action to automatically compresses JPEGs, PNGs and WebPs in pull requests, IMHO this is the best option

#WebPerf #ImagePerf #PerfTools #Image

GitHub Actions bot comment showing that images were automatically compressed by Calibre’s image-actions. The comment reports a 47.1% reduction in image size, saving 104.46 KB. A table displays one example file (‘Screen Shot 2020-09-17 at 3.29.33 pm.png’) reduced from 221.87 KB to 117.41 KB. It notes that 348 images did not require optimisation, and includes a ‘View diff’ link for visual comparison.

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Reposted by Joan León

SquiggleConf @squiggleconf.com · Aug 22

Want to debug your web app’s performance? DevTools has the answers: you just need to know where to look. @rviscomi.dev explains the hidden, upcoming, and all-around useful features of the Performance panel at SquiggleConf 2024.

youtu.be/nJ-h7UWdXZA

The Chrome DevTools Performance Panel | Rick Viscomi

YouTube video by SquiggleConf

youtu.be

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Reposted by Joan León

Harry Roberts @csswizardry.com · Aug 22

👀 I’ve been working on a little something! There’s a link to the demo in the video description.

www.youtube.com/watch?v=IMww...

Obs.js Preview – Adapt to user context

YouTube video by Harry Roberts

www.youtube.com

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Joan León @nucliweb.net · Aug 21

Test TTFB From Multiple Test Locations
www.debugbear.com/test/ttfb
by @debugbear.com

TTFB Test: Check Time to First Byte On Your Website

Measure Time to First Byte performance from multiple global test locations.

www.debugbear.com

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Joan León @nucliweb.net · Aug 21

Do you have a website with international visitors?

Check the Time to First Byte (TTFB) from different locations, and create a plan to improve it if your visitors are having a bad experience.

Start testing today, links in the first comment.

#WebPerf #PerfTools #Performance #TTFB

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Joan León @nucliweb.net · Aug 14

🔍 Found in a recent web performance audit:
favicon.ico → 301 redirect → broken URL → returns 13 MB uncompressed HTML

⚠️ Even tiny assets can slow your site if misconfigured.
Check static files (favicon, images, CSS, JS) — small issues add up

#WebPerf #WebPerformance #Frontend #DevTips

A screenshot of a web browser's developer tools, specifically the network tab, showing the details of a network request for a "favicon.ico" file. The view is split into two main sections. The left section, under the "Request" heading, details the HTTP GET request, including the URL https://www.**********/favicon.ico (with the domain name obscured). The right section, under the "Response" heading, shows the server's response details. The highlighted information includes "Status: 200", "Transmitted Size: 1.19 MB", "Full Size: 13.0 MB", "Content Type: text/html; charset=utf-8", and "Request Duration: 3.46 s".

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Reposted by Joan León

Harry Roberts @csswizardry.com · Aug 13

🇪🇪 🇨🇦 🇪🇸 🇮🇳 🇿🇦
Building quite the community over here! Get involved:

csswizardry.gumroad.com/l/subscribe

Subscribe

I’ve been writing or creating content in some form or another since 2009. Some of you have been with me since the very beginning. That over 15 years!The articles and research I publish on csswizardry....

csswizardry.gumroad.com

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Joan León @nucliweb.net · Aug 11

It's a great project 🙌

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Reposted by Joan León

Bart Veneman @veneman.dev · Aug 11

I appreciate all 18 of you! +1 rank gained is still a plus in my book.
2025.stateofcss.com/en-US/other-...

State of CSS result table showing the "other tools" section. Project Wallace is listed near the bottom with 0.5% of respondents (18 people) indicating they use it. A tooltip says there's a +1 increase in rank.

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Joan León @nucliweb.net · Aug 11

It’s the idea of option 3, thank you for the feedback 🫶

2

Joan León @nucliweb.net · Aug 10

As a techie, I totally agree.

I’d love to hear the perspectives of people from SEO, Marketing, UX, Product, and Management.

2

Joan León @nucliweb.net · Aug 10

In a Web Performance book, when technical references are made, which would you prefer?

1️⃣ Link to external refs, keeping reading high-level
2️⃣ Go into detail with the tech explanation
3️⃣ Both, deep dive in a distinct visual format so it can be skipped if desired

e.g.: Avoid long tasks in JavaScript

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Joan León @nucliweb.net · Aug 8

I'm in ☺️

Harry Roberts @csswizardry.com · Aug 8

🧑‍💻 I wasn’t going to mention this until next week but it’s Friday—treat yourself!

I’ve just launched a members-only subscription: screencasts, Q&A, mentoring, discounts, and more.

👉 csswizardry.gumroad.com/l/subscribe

Subscribe

I’ve been writing or creating content in some form or another since 2009. Some of you have been with me since the very beginning. That over 15 years!The articles and research I publish on csswizardry....

csswizardry.gumroad.com

Joan León @nucliweb.net · Aug 7

📉 E-commerce site with LCP > 6s, INP > 2800ms, CLS > 1.1
Broken UX = lost sales.

💡 Performance isn’t just for devs.
It’s key to convert, retain, and grow.

Is your site fast enough to keep up with your customers?

#WebPerf #UX #CRO #eCommerce

Performance metrics from a web performance tool showing results for a mid-tier mobile device with a fast 4G network. The metrics are divided into Local and Field (URL) data. Under the Local tab: LCP (Largest Contentful Paint) is 3.59 seconds, INP (Interaction to Next Paint) is 319 milliseconds, and CLS (Cumulative Layout Shift) is 0.91. Under the Field (URL) tab: LCP is 6.19 seconds, INP is 2827 milliseconds, and CLS is 1.16. All values are highlighted in red or orange, indicating poor performance.

2 4

Reposted by Joan León

Andrey Sitnik @en.sitnik.ru · Aug 6

This is me a couple of days before the first release of PostCSS.

From my new article about the history of PostCSS and the lessons I learned from it (for example, how to break an API when you have 400M downloads per month).

evilmartians.com/chronicles/w...

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Reposted by Joan León

Harry Roberts @csswizardry.com · Aug 6

Same code, same infrastructure, different context. Web performance is sometimes an ‘us thing’ and sometimes a ‘them thing’. For better or worse, we have a responsibility to cater to both.

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