TL;DR: If your font file is significantly larger than 20K you may ask yourself “How did I get here?”. For images I think we (web developers) have a sense of how many bytes we can expect an image we see on a page to be. A JPEG photo? 100-ish K is ok for a decent […]

Ever wanted to look at your page and turn Web Fonts on and off? Experience the layout shift repeatedly, like some sort of UX torture? Look no further, here comes the handy bookmarklet. Install Drag this link to a bookmark toolbar near you: toggle fonts Use Go to a page with web fonts and click […]

You know the pattern: spit out some markup, probably server-side, but hide it for later. On-demand features (not to overwhelm the UI), dialogs waiting to pop, and so on. <div class=”modal hidden”>content here…<div> And what happens when the “content here…” includes resources, such as images? Is the browser going to download them? Let’s check. What […]

Remember spacer.gif? Yeah, “good” old days… We may now have all the CSS features to make everything better but sometimes the ghost of spacer gif rears its transparent head. And that’s an HTTP request. A request that’s better devoted to something useful. Like an LCP image or something, I dunno. So anyway, sometimes a simple […]

Hello, dear reader and web performance enthusiast! It’s time to sit down and write an article for the performance calendar. Here are some more details. Or if you’re not feeling like writing, look around you and recruit the person you think should share their knowledge with the world. What can you write about? Just share […]

Couple days ago I found out about a tool called pdfcpu, a PDF processor. Among its features I saw “optimize” so I had to take it ot for a spin and see how much of an optimization we’re talking about. Here’s a quick study of optimizing a random-ish sample of PDF files. Source data I […]

So I woke up yesterday being scolded by Google. An email from Google Search Console Team with subject “Core Web Vitals INP issues detected on your site”. Huh?! It was about this WordPress-powered site that you’re reading now (phpied.com). The Interaction to Next Paint metric (INP for short) was in the “Needs improvement” category as […]

Inspired by Harry Roberts’ research and work on ct.css and Vitaly Friedman’s Nordic.js 2022 presentation, Rick Viscomi hacked up a tool (a JS snippet) called capo.js that can do what Harry says. Next logical step is to test the results of the tool in a no-code experimental setting and see if the results make sense […]

Lighthouse (LH), the performance auditing tool from Google now has a diff tool so you can compare what happens before/after a change or me vs competitor types. And WebPageTest.org (WPT), the industry-darling web perf analyzer, also runs Lighthouse and in addition to presenting the results (in two different ways, actually) you can export the results […]

Adam Fendrych reported that Scott Jehl said in his Web Expo talk that a website should load before you can say “Cumulative Layout Shift”. What does that mean in practice? We’re web performance specialists here, we work with measurements and numbers, so we need a more exact number. Numbers reduce ambiguity. To find out that […]

Chrome is making a change on how Largest Contentful Paint (LCP) core web vital (CWV) is being calculated in order to avoid abuse. The abuse is that people cheat by putting a fake “hero” image (imagine a stretched out 1×1 transparent gif) and have this counted as a sooner LCP event. Chrome is fighting this […]

“When I was younger, so much younger than today” and upset and full of vinegar about the state of the world, I’d say things like “CSS is the worst” (not really). Now, half a year later, older and wiser and more accepting, I’d agree to mellow down to “CSS is render-blocking”. Un-render-blocking CSS What this […]

Helloooo, dear reader and web performance enthusiast! It’s time to sit down and write an article for the performance calendar. Here are some more details. Or if you’re not feeling like writing, look around you and recruit the person you think should share their knowledge with the world. What do you want to write about? […]

Thomas Steiner has a brilliant idea for this year’s Perfplanet calendar edition: what if we revisit some of the best articles from the past. “Best” is subjective but how about “still popular”? So here’s a list of the 31 most visited articles in the past year in reverse chronological order of publication. (31 as the […]

I was just admiring Tim Kadlec eye-pleasing site. Nice, simple, see what I’m talkin’ ’bout. The feature I liked most was the footer that said “This page loaded in 0.186 seconds”. First of all – fast! Second – I thought all sites should have that. And what better way than an on-demand bookmarklet you carry […]

Helloooo! It’s time to sit down and write an article for the performance calendar. You have until Nov 30 to send me your piece. Details. What do you want to write about? Some ideas: Hello, 2007 called! Do I still shard domains to load resources from? Do I still package all JS in one big […]

I’ve been trying to stay away from webfonts as much as I can. IMO they are not worth the performance complications. Font loaders, FOUT, yadda-yadda. But… it happens. Story time While showing off another one of my music theory exercises to my prof, he mentioned it would be nice to be able to tell v […]

I’m sure better tools exist, but hey, quick and dirty is faster: running a quick console thing to tell me what makes the HTML payload bigger

TL;DR: Please start writing and finish before Dec 1st. Amazingly http://calendar.perfplanet.com has been up for 7 years straight now, helping spread the word about web performance and helping the developers do their best to provide fast and pleasurable experiences. Every year people from all walks of development life come to the calendar where an article […]

Beacons are small requests that our apps make to report some information “home”, to the server. Beacons are often used to report visitor stats, JS errors, performance metrics. Beacons often don’t return any data back to the client, but some do. Example use <div id="app">Awesome app is awesome</div> <script> // gather data somehow var data […]

On my way to NYC for Edge conference and NYC Web perf meetup. Some slides and RSVP links inside.

I gave a talk about React at BrazilJS few days ago. The “slides” are here. In this post I’ll go over what I said (more or less) at the beginning of the presentation. I hope to follow up with some more code. Disclaimer: I work at Facebook. But these are my thoughts. In fact, I […]

So I’ve been part of the quest of making all Facebook social plugins faster, even if it means rewriting them from scratch. After the Send plugin, Like button (perf optimizations described here), Follow plugin, Facepile and Likebox (perf details here), now you have a faster Recommendations plugin. The techniques used to make it faster are […]

This excellent Google I/O talk mentions that Chrome for Android moves the CSS animations off of the UI thread, which is, of course, a great idea. Playing around with it, here’s what I found: Browser support: Desktop Safari, iOS Safari, Android Chrome. You need to use CSS transforms. Animating regular properties doesn’t work. Update: (see […]

Problem: too much JavaScript in your page to handle 3rd party widgets (e.g. Like buttons) Possible solution: a common piece of JavaScript to handle all third parties’ needs What JavaScript? If you’ve read the previous post, you see that the most features in a third party widget are possible only if you inject JavaScript from […]