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Rick Viscomi Profile picture
@rick_viscomi
Nov 22, 2019 • 6 tweets • 4 min read • Read on X
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Next at #perfnow, @patmeenan professes his contempt for web fonts, and something something HTTP/2 😁 ImageImage
How to test for H2 prioritization issues with @usingwpt Image
Patrick Meenan and the Waterfalls of Doom #perfmatters ImageImageImageImage
Check out @tunetheweb's HTTP/2 chapter in the Web Almanac for a comprehensive look at the state of the web

These slides brought to you by @patmeenan's WebPageTest School of Design: "all skills, no frills"

We love you Pat 😁 ImageImageImage
Sage advice: "when you see weird shit in your waterfalls, ask why" Image

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More from @rick_viscomi

Rick Viscomi Profile picture
Feb 6
The @HTTPArchive website was passing the Core Web Vitals assessment in PSI, but there was a problem

p75 INP was 232ms, missing the good threshold by a bit

With INP only weeks away from becoming a CWV, this was a big liability and the site would soon start failing the assessment

PSI screenshot, passing the CWV assessment
Warning icon saying that the assessment is liable to change when INP replaces FID in March
p75 INP 232ms, 72% of experiences are good, missing the threshold
So I looked at the site's performance in the Core Web Vitals report of Search Console

Search Console corroborated what PSI was telling me: the site has an INP issue

But there was another clue: the home page, which was the only one that had URL-level data, was fast (110ms) Screenshot of Search Console reporting 14 URLs with INP issues, group INP of 232ms, and home page INP of 110ms
The next few sample URLs that didn't have sufficient data were the report pages, like this one:



These are more complex, interactive pages, so if there are INP issues on the site, this would be where it's coming fromhttparchive.org/reports/state-…
Read 22 tweets
Rick Viscomi Profile picture
Feb 5
🔥 INP resource megathread 🔥

Here's a list of resources to help you on your journey to optimize #INP and get ready for it to become a #CWV next month
The first place to go with general questions about INP should be the official docs at

Here you'll find answers to basic questions about the metric as well as links to other helpful resourcesweb.dev/inp
💡 Tip: Check out to explore the collection of INP resources at a glance

- what it measures
- how to measure it (lab and field)
- how to optimize it (JS and rendering)
- successful case studies web.dev/explore/how-to…
Image
Read 35 tweets
Rick Viscomi Profile picture
Jul 15, 2021
📝 New post with @felixarntz: The performance effects of too much lazy-loading

The bottom line is that lazy-loading LCP images can make them slower. Don't do it!

Learn more about our analysis 👇
web.dev/lcp-lazy-loadi…
@felixarntz Specifically looking at img[loading=lazy], adoption is at 17% of websites, up from 1% this time last year.

Of those 17% of websites, 84% are @WordPress websites! Pie chart showing WordPress...Timeseries chart of lazy-lo...
@felixarntz @WordPress When we look at how real users' LCP experiences compare on WordPress sites with and without loading=lazy, we see something peculiar:

LCP seems to be slower when lazy-loading is used 🤔 Box and whisker chart showi...
Read 10 tweets
Rick Viscomi Profile picture
Jun 17, 2021
Here's a head-scratcher for you: why is example.com failing the Core Web Vitals assessment despite getting perfect lab scores? It's just a KB of text!

This is a good teachable moment in reading web perf tools. PageSpeed Insights results for example.com, 100 Lighthouse s
Lab tests are run from a single location at a point in time. Lighthouse in PSI emulates a relatively low-end phone and the site performs very well, getting a lab performance score of 100 and 0.8 second LCP.

So far so good.
Field data is a distribution of real-user experiences aggregated over time.

Good lab tests today may not be simulating poor real-user experiences from a couple of weeks ago. So the field data may be dragged down until the poor experiences are "flushed" out of the 28-day window.
Read 10 tweets
Rick Viscomi Profile picture
Oct 2, 2020
Core Web Vitals tip: CLS can come from unexpected places, like headers that become fixed or sticky positioned to the top of the page on scroll.

By removing the header from the layout flow and sticking it to the top of the page, all of the subsequent contents shift up.

(1/4)
And when scrolling back to the top of the page, the header is added back into the layout flow, causing YET ANOTHER layout shift.

This kind of CLS is unbounded, meaning users can incur many layout shifts depending on their scrolling behavior, and it can be hard to debug.

(2/4)
The solution for this and most other layout stability issues is to reserve space for the header when it becomes pinned, for example with a placeholder element or margin-top on the next content.

Check out web.dev/optimize-cls for more tips.

(3/4)
Read 4 tweets
Rick Viscomi Profile picture
Jul 26, 2020
Resharing two #a11y episodes I did for the State of the Web series on today's 30th anniversary of the Americans With Disabilities Act.

In January 2019 I spoke with Nektarios Paisios from the Chrome Accessibility team about making the web more accessible.
…theweb.googledevelopers.libsynpro.com/accessibility-…
And in January 2020 I revisited the topic with Marcy Sutton, Head of Learning at Gatsby.

I *highly* recommend giving both of these a listen to learn about the state of accessibility from two different perspectives.

…theweb.googledevelopers.libsynpro.com/video-with-dou…
Alternatively, here are links to the YouTube videos of each episode, which include captions.

Nektarios:
Marcy:
Read 4 tweets

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