Author Archive

The Truth(tm) about encoding SVG in data URIs

Feb 9th, 2024

tl;dr: You can stop worrying and URL-encode only the # character. What? So you want to have an SVG image in a CSS stylesheet. Yup, using data URIs (hey lookie, a 2009 post). There are a number of reasons not to embed images in CSS to begin with (caching, reuse), but hey, sometimes you’re not […]


How many bytes is “normal” for a web font: a study using Google fonts

Jan 23rd, 2024

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 […]


Font-face toggler bookmarklet

Jan 8th, 2024

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 […]


Image requests in hidden content

Jan 1st, 2024

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 […]


Minimum viable no-image image src

Dec 26th, 2023

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 […]


Perfplanet calendar ’23 call for articles

Nov 2nd, 2023

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 […]


A quick study of PDF optimization

Aug 17th, 2023

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 […]


Running JPEG-XL tools on shared Dreamhost

Jul 20th, 2023

Let’s see how to setup and run cjxl (and its sibling djxl) on a simple shared hosting provider so you can encode and decode JPEG-XL (aka JXL) images. How There are better ways to install libjxl and its command-line tools but they require you to have sufficient privileges on your computer or server. With inexpensive […]


Fixing INP with a VIEWPORT tag

Jul 12th, 2023

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 ( The Interaction to Next Paint metric (INP for short) was in the “Needs improvement” category as […]


A circle of web performance innovation

May 21st, 2023

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 diff + WebPageTest

May 9th, 2023

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 (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 […]


Jehl’s Law of Web Performance

Apr 21st, 2023

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 […]


Quick BPP (image entropy) check

Apr 13th, 2023

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 […]



Jul 26th, 2022

Details from a talk to NYWebPerf meetup will go here after the talk. For now there’s: with the code and slides


Faster WordPress rendering with 3 lines of configuration

Jul 2nd, 2022

“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 […]


Write to an Airtable with PHP

Feb 21st, 2022

Lately I’ve been rediscovering the joy of PHP. Also been helping an MVP get off the ground which uses a lot of nocode/lowcode bits and pieces and miraculously puts them together. Anyway, I had to write to an Airtable table with PHP and some quick googling didn’t find an example to copy-paste so I’m writing […]


Perfplanet calendar ’21 call for articles

Nov 26th, 2021

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? […]


Perfplanet calendar’s oldies but goodies

Nov 3rd, 2021

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 […]


ffmpeg: make a video with a static image and an audio file

Jul 6th, 2021

tsia ffmpeg -loop 1 -i image.png -i audio.mp3 -c:a copy -c:v libx264 -shortest result.mp4


Video grids with ffmpeg

Dec 7th, 2020

I wanted to create a video that is a 3×2 grid of 6 other videos. This one to be precise: I was hoping I can use ffmpeg, because the thought of using a proper video editing software gives me the chills. In fact at some point I thought things will require iMovie and went to […]


Randomizing music with MuseScore and Node.js

Sep 13th, 2020

One of my esteemed professors from Santa Monica College, Dr. Driscoll asked for an opinion on how one can use a sheet of music and reshuffle some measures to generate a unique exercise for each student. This turned out more fun than anticipated and here’s a solution I came up with using the free notation […]


Natively lazy-loading Facebook social plugins

Jul 24th, 2020

tl;dr: Add data-lazy=”true” to your Facebook social plugins that are below the fold and reap the benefits. In code: // before <div class=”fb-like” data-href=””></div> // after <div class=”fb-like” data-href=”” data-lazy=”true”></div> The following 18 seconds video demonstrates the difference. Where currently your visitors load Facebook iframe content even if it’s way down the page, after you […]


Life after Facebook?

Jul 14th, 2020

Yesterday was my last day at Facebook. After 9 1/2 years it was high time for a change. I dropped the news on twitter/fb and thought now it would be nice to answer the question of “what’s next?” that friends are wondering. The trajectory I myself have wondered sometimes what the life after Facebook could […]


A programmer’s job dimensions

May 14th, 2020

I’m not the one who philosophizes often in public, but indulge me this thought on the types of work we do as programmers and feel free to add your own dimensions. I’ve thought about how sometimes I like to work on user-facing products and sometimes on developer-facing ones. Real products that my mom can see […]


WebAudio Deep Note, part 5: gain node

Nov 9th, 2019

Previously on “Deep Note via WebAudio”: intro play a sound 2.1. boots and cats loop and change pitch multiple sounds nodes In part 4 we figured out how to play all 30 sounds of the Deep Note at the same time. The problem is that’s way too loud. Depending on the browser and speakers you […]