Stoyan Stefanov

Happy to report that after I published a plain old HTML page explaining how to create URLs for my app, now both chatgpt and gemini can do it. Not sure how quickly it happened, but they did learn.

My blogging raison d'être is mostly "note-to-self", not trying to be popular or thought-leader-y. And every once in a while it helps me, even when I forget that I have a problem I've solved previously.

youtube.comGive JXL a ChanceYouTube video by stoyanify

Time to retire my rant? www.youtube.com/watch?v=VJaa... 'cuz JPEG-XL is now in Chrome! developer.chrome.com/blog/jpeg-xl...

sightread.orgSightRead.org - Free Sight Reading PracticePractice sight reading with customizable exercises. Generate random rhythmic patterns, use the metronome, and improve your music reading skills. Free, no login required.

My example of "AI is amazing! (at things I don't know anything about)" For my SightRead.org project I use a font called MusGlyphs. The thing is I needed a glyph that is not in the font. Emailed the author, he suggested I just go for it in a font editing tool. FontForge is what I used and ...

... and it's a tad intimidating for a noob like me. I kept needing new glyphs and my progress and releases slowed down because of "oh man, need to edit that font again" procrastination. Enter Claude. Not only it added a couple of glyphs I needed, after a minimal handholding, but...

...but I asked it to go back and fix the ones I added manually, using consistent spacing, fixing warnings, etc. Turns out .sfd files (source of my font's WOFF2 subset exports) are not binary but human-readable text files full of coordinates and transforms and such vector-y things. Easy-peasy!

phpied.comDebugging download initiatorI was recently debugging why an image was being downloaded. In Chrome devtools, in the network panel, the column for "initiator" was pointing to the end of the HTML document. But that wasn't true and ...

Blog post where I was wondering why Chrome devtools is not showing me the correct initiator for an image download. And I think it's the `scheduler.yeild()` to blame. www.phpied.com/debugging-do...

My friend Javor Vatchkov just launched bandscheck.com, a nice way to see who's playing in your area tonight and in the future. Fun way to discover new artists too, thanks to audio (video) sample of each artist's work. Give it a spin!

"Do I still have a job?" check, Oct 1, 2026. Answer: yes. Chasing the source of an image request with Claude offered two (annoyingly confident, but still) dead ends. Old school poke in the profiler trace had the answer within a minute or so....

Devtools' confusing attribution of the initiator didn't help either. A repro/blog post coming...

america.gov vs gov.uk on my iPhone 8 (Safari 15). Watch this talk www.youtube.com/watch?v=VdBx... by @therealnooshu.bsky.social Hobbs about what happened during the pandemic, people desperately looking for gov't info and browsing with horrible connections on devices such as ...

... such as an old Playstation. Accessibility of info first, skeleton UIs last, please.

phpied.comllms.txt: agent-optimization wishful thinkingCan't remember where I stumbled upon a SEO-type guide that was suggesting agent-optimization via a robot.txt-like file llms.txt which lives in the web root and helps agents use your site. Perfect, I t...

Blog post where I look at my server logs, trying to answer the question: does `llms.txt` in your root help at all? www.phpied.com/llms-txt-age...

csswizardry.comUnattributed Navigation Overhead (UNO) Is Underrated – CSS WizardryUnattributed Navigation Overhead exposes the part of Time to First Byte that Navigation Timing cannot explain, including hidden cross-origin redirects.

Blog by @csswizardry.com reminding us about the UNO metric @timvereecke.bsky.social introduced on the web performance calendar csswizardry.com/2026/08/uno-... UnO = Underrated Observables 😜

calendar.perfplanet.comContributePassionate about a topic? Working on a new tool? Have a technique you want to teach? Research you've done? Tell the web performance community! Send your articles to ssttoo@ymail.com. Please include: ...

Speaking of the web performance calendar... December is a-approaching, what are YOU going to write about? calendar.perfplanet.com/contribute/

When does California's 1-click-unsubscribe law starts being mandated? Trying to cancel a subscription: website's subs management is under construction, no one is picking up the phone and AI chatbot is the only thing responding. Of course it sends you to the phone. Arghh! p.s. avoid JustFoodForDogs

Todor Zhivkov, leader of communist Bulgaria 1956-1989, "wrote" an insane amount of books, over 50 probably, fat ones too. Of course, it's really hard to write that much, even for full-time prolific folks like Stephen King or Isaac Asimov...

phpied.comI am now an Instagram Micro-InfluencerAMA. What's a "Micro-Influencer"? Someone with 10K or more followers. Approximately 15% of all Instagram accounts. So I'm a "15 percenter" What's an Instagram? A window on your baby television tha...

...These books were most certainly entirely ghost-written. The joke back then was: he's written more books than he's read. And now, thanks to LLMs, this could be you too! Even without an army of ghosts. What a time to be alive!

New blog post about becoming a Micro-Influencer on Instagram: www.phpied.com/i-am-now-an-... (meaning 10K followers) How I got there (not hard, just persistence for 5+ months) and what are the benefits (not monetary or any real influence). AMA.

@henrihelvetica.bsky.social

Hello bonjour bsky, it's been a while!

Stoyan Stefanov reposted

Henri Helvetica 🧑🏾‍🚀🇭🇹

15 Mar

SIR @stoyan.me and I just hanging out. Published sooooooon....

phpied.comQuick and dirty lintingThis post is another installment of the series dedicated to building sightread.org. Parts 1, 2, 3, 4, 5, 6. I've been using TypeScript (actually JSDoc + tsc --noEmit) as my linter for a while. Well, ...

13 Feb

New blog in the series about building SightRead.org www.phpied.com/quick-and-di...

sightread.orgAsymmetric time signatures - SightRead.org BlogPractice rhythms in 5/8, 7/8, and 11/8 with flexible beat groupings that make these meters feel natural.

11 Feb

sightread.org/blog/asymmet... Adding support for 7/8 and family to my music sight reading project

phpied.comMeasuring SVG rendering timeThe questions Is rendering large SVGs significantly slower than smaller ones? Is there a cut-off size above which things are terrible? And what if these SVGs were PNGs, just for giggles. To answer t...

5 Feb

New blog post about an experiment in measuring how rendering times are affected by the size of SVGs www.phpied.com/measuring-sv...

phpied.comOops, I build.js'd it againWho amongst us has not created a blogging software of some fashion or another? I know I have, many times. My latest (joke-y) attempt was Lizzy.js. The desire to go into a writing mode and don't worry ...

24 Jan

New blog post www.phpied.com/oops-i-build...

sightread.orgIntroducing Quests and Rhythmic Dictation - SightRead.org BlogSightRead.org now has quests. Rhythmic Dictation is a new mode where you hear a rhythm and try to identify it.

21 Jan

I don't think there are many music dictation apps out there, but here's v1 of mine. Rhythm-only for now, part of the sightread.org project. To try sightread.org?rhythm-dicta... To read the blog post sightread.org/blog/quests-...

Stoyan Stefanov reposted

Martin Michalek

@machal.bsky.social

13 Jan

7 tips for your #WebPerformance education: Every December, @stoyan.me publishes the excellent Web Performance Calendar. It is a great collection of insights from the world's top experts. Even in 2026, these articles are a "must-read." Here is what caught my eye this year (thread). ⤵️

wearedevelopers.comAI is an Electric Bike for the Brain - Stoyan StefanovStoyan Stefanov calls AI an electric bike for the brain. But he warns it can also lead you straight off a performance cliff.

14 Jan

look ma' I'm now opining about AI like the big kids www.wearedevelopers.com/en/videos/17...

phpied.comType checking without the muckThis is part 4 of a series about hacking on sightread.org with minimal tooling/building and maximum web platform-ing: Part 1: Import JavaScript like it's 2026 Part 2: Maximally Minimal Build Proc...

12 Jan

New blog post www.phpied.com/type-checkin... This is now part 4 of something I thought will be a quick note. Installment 4 talks about type checking without TypeScript. Hello JSDoc! And so the DIY-ing continues until morale improves!

Stoyan Stefanov reposted

Stefan Judis

@stefanjudis.com

5 Jan

Huge congrats and kudos to @stoyan.me for running it and to all the authors for writing articles for this year's Web Performance calendar. calendar.perfplanet.com/2025/ The quality was very high, and it feels like every second post was a banger!

calendar.perfplanet.com2025 ArchivesThe speed geek's favorite time of year

phpied.comMaximally Minimal Build ProcessIn my previous post I described how I set up sightread.org with no build process and modern JavaScript. The goal was raw ES modules, no transpilation, no bundling, just <script type="module"> and we'r...

4 Jan

New blog post: www.phpied.com/maximally-mi... It's about staying away from most everything the JS ecosystem has to offer and stick close to the web platform. A build is still necessary because of long lived caches and updates but it can be tiny and simple. Time will tell how this strategy plays out

Stoyan Stefanov reposted

Brian Alfaro

@designbaa.bsky.social

1 Jan

Let's make 2026 the year to make web simple again. Not everything needs to be an app, sometimes its just idk a website. 🥳🥳

Stoyan Stefanov @stoyan.me

Web Performance Calendar day 31 article 5/5: @infrequently.org investigates SPA usage patterns showing that users often trigger only ~1 soft navigation per page load. If the heavy upfront JS costs aren’t being amortized, what are SPA's performance benefits? calendar.perfplanet.com/2025/the-cur...

calendar.perfplanet.comThe Curious Case of the Shallow Session SPAsBuried at the end of this year's instalment of my semi-annual series on network and device reality is a mystery: multiple, independent data sets from the Web Performance community indicate sites built...

Stoyan Stefanov reposted

Ben Schwarz

@benschwarz.bsky.social

@iplayoddball.bsky.social

People like to say “once the single page app is booted, it’s faster”, but they’re wrong — stats show few subsequent navigations occur. React simply isn’t worth the cost for most websites.

Stoyan Stefanov @stoyan.me

Stoyan Stefanov reposted

Greg Strange

calendar.perfplanet.comChrome DevTools Features I Use All the Time (and Why You Should Too)Most developers open Chrome DevTools, check a couple of network requests, maybe refresh the page once or twice — and that's it. I used to do the same. Over time, DevTools became something else entir...

I almost slipped this article because that headline is usually a red flag to me. But I'll be damned, every single one of these features slap.

Stoyan Stefanov @stoyan.me

Web Performance Calendar day 31 article 2/5: @keerthanak17.bsky.social on making friends with Chrome DevTools and transforming it into a powerful tool for deep understanding, debugging, and improving of real-world web performance calendar.perfplanet.com/2025/chrome-...

Stoyan Stefanov reposted

Ryan Townsend

@twnsnd.com

calendar.perfplanet.comFrom Theory to Tiny: Implementing Compression DictionariesCompression Dictionary Transport became an official IETF Proposed Standard this September (congratulations to Yoav Weiss & Pat Meenan 🎉). If you don't know what they are, I recommend watching Pat's wo...

Put the NYE champagne down… my article is up on the 2025 Web Performance Calendar 🥳

Stoyan Stefanov @stoyan.me

Web Performance Calendar day 31 article 4/5: @twnsnd.com on Compression Dictionaries to dramatically shrink responses (60–90% smaller than Brotli/GZIP). Why adoption is slow. Practical architectural decisions and implementation tips to get huge bandwidth wins. calendar.perfplanet.com/2025/from-th...

Stoyan Stefanov reposted

Peter Bowyer

@peterbowyer.bsky.social

Replying to @stoyan.me

@stoyan.me it's been a fantastic Web Performance Calendar, thank you for curating it and Happy New Year!

Stoyan Stefanov reposted

Vinicius Dallacqua

@webx.bsky.social

agent.perflab.ioPerfAgent - AI-Powered Web Performance AnalysisGet expert insights on Core Web Vitals and performance optimization from an AI specialized in web performance analysis.

Wrapping up the year with my article for the Perf Calendar with my write up about how I ended up creating agent.perflab.io! It has AI, it has Perf…what else could you want 😎🔥 I’m always happy to see my content in the Performance Calendar! Thanks for the initiative @stoyan.me !

Stoyan Stefanov @stoyan.me

Web Performance Calendar day 31 article 3/5: Can AI meaningfully help with real-world performance analysis? @webx.bsky.social explores how to train AI/LLM agents to interpret complex browser data (like DevTools traces) into actionable insights. calendar.perfplanet.com/2025/teachin...

calendar.perfplanet.comTeaching Agents about Performance insightsAI is kinda everywhere! Everyone is shipping AI features or Agents, but few of those systems can reason about the complex reality of performance data. This session is a deep dive story into the jour...

Web Performance Calendar day 31 article 1/5: Tsvetan Stoychev shares that BasicRUM (open-source Real User Monitoring tool) will have its source code released Q1 2026. Self-hosted, privacy-friendly, with AI-powered insights & dashboards to spot perf issues calendar.perfplanet.com/2025/open-so...

calendar.perfplanet.comOpen Source RUM with BasicRUMIt's been a long, busy year but my friend Faisal and I stayed focused on building BasicRUM. After work, we pushed countless commits from a cozy café in Munich. The important news is that we're wrappi...

calendar.perfplanet.com7 Steps of a Web Performance JourneyThis year, Sergey Chernyshev, Eric Goldstein, and Alex Chernyshev - members of the NY Web Performance meetup - decided to collaborate on the future of the UX Speed Calculator tool Sergey created a few...

30 Dec 2025

New blog post about subsetting a ligature-heavy font highperformancewebfonts.com/read/subsett... Almost always we subset based on text. But in my case, a more fine-tuned glyph-based approach saves 91% of bytes as opposed to 74% in the usual way. Worth it?

Stoyan Stefanov reposted

Sergey Chernyshev

@sergeyche.dev

30 Dec 2025

Our Web Performance Journey guide is live on PerfPlanet Calendar!

Stoyan Stefanov @stoyan.me

Web Performance Calendar day 30 with @sergeyche.dev, Eric Goldstein and Alex Chernyshev on mastering perf: get business to care, link UX speed to outcomes, set thresholds, understand real users with percentiles, trends, distributions, tie to business metrics calendar.perfplanet.com/2025/7-steps...

I added a little feature to sightread.org to remove the chrome so I can screen-record exercises UI-free and post them as Instagram reels. This way folks can squeeze a bit of practice while scrolling. If that sounds like you: www.instagram.com/sightreadorg/

sightread.orgSightRead.org

Stoyan Stefanov reposted

Paul Calvano

@paulcalvano.bsky.social

29 Dec 2025

My contribution to this years Web Performance Calendar is all about Third Parties and Single Points of Failure (SPOF). Based on @httparchive.org data I found that 67% of websites have at least 1 render blocking third party - and quite a few of them are SPOF risks!

Stoyan Stefanov @stoyan.me

Web Performance Calendar day 29 with @paulcalvano.bsky.social's research on 3rd parties, SPOF, and the need to test and monitor these. 67% of sites out there have at least 1 render-blocking external dependency. calendar.perfplanet.com/2025/third-p...

calendar.perfplanet.comThird Parties and Single Points of FailureYou've heard it many times - third party content can easily cause an otherwise well performing website to become sluggish and slow. And depending on how this content is loaded, it can also introduce s...