@hunkemoller.bsky.social: UX Score 93 to 48 after a platform migration.

CLS: near-zero → 0.18 (elements jump around)
INP: 120ms → 419ms (every tap feels sluggish)

New platform, new features, measurably slower for every visitor.

No replatform should ship without matching the old site on every CWV.

Check your field CLS: iron-out.io/benchmark/
Guide: iron-out.io/core-web-vitals/cls

#WebPerf #CLS

Client site: UX Score 90+. Green across the board. Fast.

Except the checkout. CLS: 0.7. Payment selector loads late, form fields jump, users type into the wrong field.

Shows up as "checkout abandonment on mobile." Nobody looks at layout shifts.

Check CLS on your checkout, not just the homepage.

The hardest part of performance work isn't knowing what to fix. It's getting approval to fix it

Our tool shows estimated revenue you're leaving on the table from performance issues

Not what you'd gain. What you're losing

Q2planning deadlines are now. Run before the meeting.
iron-out.io/benchmark/

Coolblue vs Bol, web performance comparison:

Bol.com: UX Score 100
Coolblue: UX Score 93

Both strong. But the 6-month per-metric trends show where each improved or regressed.

Our compare tool shows sparklines for each CWV, threshold lines, and shareable URLs.

See iron-out.io/benchmark/compare

Audit finding: 2 sprints on image optimisation, zero LCP improvement.

LCP sub-parts breakdown told the story:
- TTFB: 2.1s
- Resource Load Delay: 1.4s
- Resource Load Duration: 500ms (already optimised)
- Render Delay: 200ms

TTFB was half the LCP budget. Once that was addressed → LCP 1.6s.

Free UX Score Check — Website Performance Benchmark Check your UX Score for free. Real CrUX data across LCP, INP, CLS, TTFB and FCP. Benchmark against the top 300 Dutch websites. No login required.

Your website has a UX Score and you've probably never seen it.

It's based on real Chrome user data from real visits. Not a lab test. Not a guess.

Enter any URL, get your score in 10 seconds: www.iron-out.io/benchmark

Free. No login 🚀

Why we should stop talking performance metrics to Business Leaders Web performance is a lot like walking on those moving walkways at the airport. When it moves smoothly, you barely notice it. You feel fast. Supported. In control. But when one section stutters, even ...

Web Performance Calendar day 16 with @sandervs.bsky.social on why the word "millisecond" doesn't belong in the boardroom

calendar.perfplanet.com/2025/why-we-...

Improve TTFB and UX with HTTP streaming If you have a statically generated website hosted on a CDN, it’s probably very fast (unless you add too much client-side JavaScript). However, for dynamically generated pages that load content from a...

Web Performance Calendar'25 day 1 with @mb21.bsky.social on HTTP streaming in the world of HTTP2/3 and Node. Mauro shows us how to start rendering earlier, turning a slow (full) page load into a progressive experience using db.stream() in JavaScript

calendar.perfplanet.com/2025/improve...

Traffic Modeling Using Machine Learning When I explain the difference between lab (aka synthetic) and field data to people, one of the things I mention is that the lab allows for testing under repeatable, controlled conditions. Each test ru...

Web performance calendar day 3 when @ethangardner.com shows us how to train a ML model on synthetic perf metrics and use it to predict approximate field data before a page/feature goes live.
calendar.perfplanet.com/2025/traffic...

Fast by Default After 25 years building sites for global brands, I kept seeing the same pattern appear. A team ships new features, users quietly begin to struggle, and only later do the bug reports start trickling in...

Web Performance Calendar day #4 when @denodell.bsky.social shows us how to adopt a fast-by-default mindset to escape the vicious cycle of ship-complain-panic-patch.

calendar.perfplanet.com/2025/fast-by...

GitHub - cloudflare/telescope: Cross-browser web performance testing agent Cross-browser web performance testing agent. Contribute to cloudflare/telescope development by creating an account on GitHub.

Telescope, the new cross-browser performance testing agent I mentioned at #perfnow that we @cloudflare.social have open-sourced is here: github.com/cloudflare/t...

We want this to be a tool the entire community is able to contribute to and benefit from, so please help us make it better!

Screenshot of the performance.now() conference schedule. Follow the link in the main text to read it.

Schedule schedule on the wall, who has the best line-up of them all?

perfnow.nl/schedule.html

🚀 Quick Performance Tip:
Not every conversion issue is a checkout issue.

Slow pages earlier in the flow mean fewer baskets and fewer orders.

#pagespeed #CRO #ux #webperformance #ecommercegrowth #digitalexperience

🚀 Quick Performance Tip:

Most sites do not lose customers at checkout. They lose them to small frictions earlier in the flow.

A blank screen, a shifting button, a slow filter. Each breaks trust. And trust is what sells.

#ecommerce #uxdesign #webperformance #CRO #pagespeed

Performance tips by sander van surksum

🚀 Quick Performance Tips (series intro):
Performance still is not a hygiene factor in e-commerce. But it should be.

Over the next few weeks I will share a short series on how flow, friction and trust shape user behaviour and sales.

#ecommerce #webperformance #conversionrate #digitalgrowth

performance.now(); 30th and 31st of October, Amsterdam On 30th and 31st of October, 2025, the sixth edition of performance.now() will take place in Amsterdam—a single track conference, covering today’s most important web performance insights.

performance.now(), the web performance conference, 30th and 31st of October, Amsterdam. Single track, the best speakers in the industry, plenty of your performance-mad peers around to have fascinating conversations. What's not to like? Let's introduce our speakers ...
perfnow.nl

Graph from CrUXVis showing LCP subparts

Google's new CrUX API updates offer deeper performance insights:

🚀 LCP Image Subparts – Find what’s slowing your LCP
📸 LCP Resource Type – Know if LCP is text or images
🌐 RTT Data – Understand network latency better

Optimize your site with these new metrics! #webperf #SEO #userexperience

screenshot of top 6 speakers at frontmania 2024 - second place Sander van Surksum

Two months ago, I spoke about INP (Interaction to Next Paint) and the scheduler.yield() at @frontmania.bsky.social -- and the feedback is in... 🥈 I was rated the 2nd best speaker at the event! 🌟 🥳 🎉

2 months ago, I gave a talk at @frontmania.bsky.social where I showcased a demo I created to highlight INP issues on a PDP page when switching colors. It showed how small delays can frustrate users and hurt conversions. Check it out: inp-demo.netlify.app/product-detail #webperf #INP #performance

Yes please, just like the reasons mentioned earlier, Safari currently feels like a black box when it comes to performance insights. Without performance APIs, we are left guessing how well a site performs for Safari users. This lack of visibility forces us to rely on speculation instead of data.

Yesterday during my #perfnow talk, I mentioned the Web Performance Slack. If you’d like to join the Slack, use this link before Nov 25: join.slack.com/t/webperf…

We finally know what Erwin looks like without his hat! #perfnow

The golden rule of performance improvement: "Always measure the impact of your changes." #perfnow

Took 2 mins at #PerfNow to talk about the RUM Community Group in W3C for anyone doing RUM. It's free and easy to join if you're interested! www.w3.org/community/ru...

On my way to @perfnow.bsky.social excited to catch all the talks! #perfnow

Goedemorgen!

It’s the 5th anniversary of @perfnow.bsky.social, one of the most well-organised events with an amazing audience! 🎉 First stop today: WebPerfDays Unconference at Google Amsterdam. Huge thanks to everyone who made this possible—let’s connect if you’re there or catch the livestream! 🚀 #perfnow

Goeiemorgen 😀 Tot vanmiddag!

Tot morgen!