Tags: performance

In the latest issue of Matthias’s excellent Own Your Web series, he describes the recent betrayal by Google:

The search engine no longer says “here, go read what this person wrote.” It now says “here, I’ve already read it for you.” The contract is broken.

He’s absolutely right.

But…

Have you ever clicked on a result from a search engine? Unless you’re lucky enough to land on a nice personal website, you’re more than likely to be confronted with pop-ups to allow tracking, or a desparate plea to subscribe to a newsletter, or just rubbish ads all accompanied by a slow page loading somewhere in the mix.

Don’t get me wrong. I’m not saying that what Google is doing is okay. But let’s not pretend that everything indexed by Google is just fine and dandy for people to visit.

And of course the main reason why websites are so terrible is because they’ve tied their business model to heaps of behavioral advertising driven by invasive tracking courtesy of …Google.

This reminds me of AMP. Remember Google AMP? It was a terrible solution to a real problem. Web pages were (and still are) bloated and slow. The correct solution would be to encourage people to fix that, but instead Google mandated a proprietary format for your content that had to be hosted on their servers.

AMP was a disaster, both in practical terms and in the reputational damage it did to Google’s developer relations.

Now they’re doing it again, powerwashing away any goodwill they ever had with site owners. Now Google doesn’t even send search engine traffic to the websites that host the ads that Google encouraged people to put on every page.

It’s almost as if Google is a company so large and with so many competing interests that it now suffers from an incurable split personality disorder.

Personally I think they’re missing a trick. They should be using “AI” summaries as a stick.

If your site is slow, or filled with user-hostile annoyances then it should be cockblocked by a hallucinated summary. But a nice fast respectful website? Send the traffic their way! Everyone wins—users, site owners, Google, the World Wide Web.

Could you imagine how quickly this would revolutionise the world of search engine optimisation? They’ve always told us that we should make websites for humans in order to get good Google juice. This would be a way of making it come true, without any of the over-engineered woefulness of AMP.

It’ll never happen of course. But I can dream.

The end of responsive images - Piccalilli

Hallelujah! Support for sizes="auto" is finally landing in Firefox and Safari! Praise be!

The Great CSS Expansion | Butler’s Log

Web development follows a familiar cycle. First we glue together a solution with whatever we have — JavaScript, image hacks, Flash, anything. Then the platform matures, and CSS or HTML eventually makes that same workaround native. Rounded corners, custom fonts, smooth scrolling, sticky positioning: all of these started as JavaScript-heavy hacks before CSS turned them into a single declaration.

We are in another one of those transition moments. A new wave of long-requested CSS features is finally landing, and many of them are explicitly designed to replace patterns that used to require JavaScript. Not as approximations — as first-class platform primitives that handle the edge cases, run in the right thread, and need zero dependencies.

The Session has been online in some form since the late 1990s. That’s long before web fonts existed.

To begin with, Times New Roman was the only game in town if you wanted serif type on a website. When Microsoft introduced Georgia it was a godsend. A beautiful typeface designed by Matthew Carter for the screen. I put it right at the start of my font stack for The Session.

Later, web fonts came along. Boy, does that short sentence belie the drama! There were very heated discussions about whether web browsers should provide this ability at all, and what it would mean for type foundries.

Microsoft led the way with their prorietary EOT format. Then everyone agreed on WOFF. Finally we got WOFF2, Electric Boogaloo.

Perhaps more important than that, we got intermediaries. Typekit, Fontdeck, and then the big daddy, Google Fonts.

That’s pretty much the state of play today. Oh yeah, and we’ve got variable fonts now.

I remember Nick Sherman presenting the idea of variable fonts at an Ampersand event years ago. I remember thinking “great idea, but it’ll never happen.” Pure science fiction. I thought the same thing when I first saw a conference presentation about a miraculous image format called Scalable Vector Graphics.

Sometimes I like to stop and take stock of what we take for granted in web browsers now. Web fonts. Variable web fonts. SVG. Flexbox. Grid. Media queries. Container queries. Fluid typography. And I haven’t even mentioned how we were once limited to just 216 colours on the web.

Georgia

Given all the advances in web typography, you might be wondering how my font strategy for The Session changed over the years.

It didn’t.

I mean, sure, I added fluid typography. That was a natural extension of my love for liquid layouts and, later, responsive design. But the font stack itself? That was still Georgia all the way.

Y’see, performance has always been a top priority for The Session. If I was going to replace a system font with a web font that the user had to download, it really needed to be worth it.

Over the years I dabbled with different typefaces but none of them felt quite right to me. And I still think Georgia is a beautiful typeface.

“But your website will look like lots of other websites!” some may cry. That used to be true when all we had was system fonts. But now that web fonts have become the norm, it’s actually pretty unusual to see Georgia in the wild.

Lora

Recently I found a font I liked. Part of why I like it is that it shares a lot of qualities with Georgia. It’s Lora by Olga Karpushina and Alexei Vanyashin.

I started to dabble with it and began seriously contemplating using it on The Session.

It’s a variable font, which is great. But actually, I’m not using that many weights on The Session. I could potentially just use a non-variable variety. It comes in fixed weights of regular, medium, semibold, and bold.

Alas, the regular weight (400) is a bit too light and the medium weight (500) is a bit too heavy. My goldilocks font weight is more like 450.

Okay, so the variable font it is. That also allows me to play around with some subtle variations in weights. As the font size gets bigger for headings, the font weight can reduce ever so slightly. And I can adjust the overall font weight down in dark mode (there’s no grading feature in this font, alas).

Subsetting

Lora supports a lot of alphabets, which is great—quite a few alphabets turn up on The Session occasionally. But this means that the font file size is quite large. 84K.

Subsetting to the rescue!

I created a subset of Lora that has everything except Cyrillic, Greek, and Latin Extended-B. I created another subset that only has Cyrillic, Greek, and Latin Extended-B. Now I’ve got two separate font files that are 48K and 41K in size.

I wrote two @font-face declarations for the two files. They’ve got the same font-family (Lora), the same font-weight (400 700), and the same font-style (normal) but they’ve got different values for unicode-range. That way, browsers know to only use appropriate file when characters on the page actually match the unicode range.

The first file is definitely going to be used. The second one might not even be needed on most pages.

I want to prioritise the loading of that first subsetted font file so it gets referenced in a link element with rel="preload".

The switcheroo

As well as file size, my other concern was how the swapping from Georgia to Lora would be perceived, especially on a slow connection. I wanted to avoid any visible rejiggering of the content.

This is where size-adjust comes in, along with its compadres ascent-override and descent-override.

Rather than adjusting the default size of Lora to match that of Georgia, I want to do it the other way around; adjust the fallback font to match the web font.

Here’s how I’m doing it:

@font-face {
    font-family: 'Fallback for Lora';
    src: local('Georgia');
    size-adjust: 105.77%;
    ascent-override: 95.11%;
    descent-override: 25.9%;
}

And then my font stack is:

font-family: Lora, 'Fallback for Lora', Georgia, serif;

It’s highly unlikely that any device out there has a system font called “Fallback for Lora” so I can be pretty confident that the @font-face adjustment rules will only get applied to browsers that have the right local font, Georgia.

But where did those magic numbers come from for size-adjust, ascent-override, and descent-override?

They came from Katie Hempenius. As well as maintaing a repo of font metrics, she provides the formula needed to calculate all three values. Or you could use this handy tool to eyeball it.

With that, Georgia gets swapped out for Lora with a minimum of layout shift.

First-timers and repeat visitors

Even with the layout shift taken care of, do I want to serve up web fonts to someone on a slow connection?

It depends. Specifically, it depends on whether it’s their first time visiting.

The Session already treats first time visitors differently to repeat visitors. The first time you visit the site, critical CSS is embedded in the head of the HTML page instead of being referenced in an external style sheet. Only once the page has loaded does the full style sheet also get downloaded and cached.

I decided that my @font-face rules pointing to the web fonts are not critical CSS. If it’s your first time visiting, those CSS rules only get downloaded after the page is done loading.

And unless you’re on a fast connection, you won’t see Georgia get swapped out for Lora. That’s because I’ve gone with a font-display value of “optional”.

Most people use “swap”. Some people use “fallback”. You’ve got to be pretty hardcore to use “optional”.

But the next page you go to, or the next time you come to the site, you more than likely will see Lora straight away. That’s because of the service worker I’ve got quietly putting static assets into the Cache API: CSS, JavaScript, and now web fonts.

So even though I’m prioritising snappy performance over visual consistency, it’s a trade-off that only really comes into play for first visits.

Next

I’m pretty happy with the overall strategy. Still, I’m not going to just set it and forget it. I’ll be monitoring the CRUX data for The Session keeping a particular eye on cumulative layout shift.

Before adding web fonts, the cumulative layout shift on The Session was zero. I think I’ve taken all the necessary steps to keep it nice and low, but if I’m wrong I’ll need to revisit my strategy.

Update: Big thanks to Roel Nieskens—of Wakamai Fondue fame—who managed to get the file size of my main subsetted font down even further; bedankt!

Constraints and the Lost Art of Optimization — Den Odell

The entire intellectual and creative output of a team that reinvented personal computing fits in a space that, today, we wouldn’t think twice about wasting on a single font file.

Somewhere in the years that followed we’ve lost the creative solutions, the art of optimization, that being constrained in that way produces.

The best engineers I’ve worked with carry this instinct even when others might think it crazy. They impose their own constraints. They ask what this would look like if it had to be half the size, or run twice as fast, or use a tenth of the memory. Not because anyone demanded it, but because just by thinking there could be a better, more efficient solution, one often emerges.

Performance-Optimized Video Embeds with Zero JavaScript – Frontend Masters Blog

This is a clever technique for a CSS/HTML only way of just-in-time loading of iframes using details and summary.

JS-heavy approaches are not compatible with long-term performance goals

Frameworks like React are often perceived as accelerators, or even as the only sensible way to do web development. There’s this notion that a more “modern” stack (read: JS-heavy, where the JS ends up running on the user’s browser) allows you to be more agile, release more often with fewer bugs, make code more maintainable, and ultimately launch better sites. In short, the claim is that this approach will offer huge improvements to developer experience, and that these DevEx benefits will trickle down to the user.

But over the years, this narrative has proven to be unrealistic, at best. In reality, for any decently sized JS-heavy project, you should expect that what you build will be slower than advertised, it will keep getting slower over time while it sees ongoing work, and it will take more effort to develop and especially to maintain than what you were led to believe, with as many bugs as any other approach.

Where it comes to performance, the important thing to note is that a JS-heavy approach (and particularly one based on React & friends) will most likely not be a good starting point; in fact, it will probably prove to be a performance minefield that you will need to keep revisiting, risking a detonation with every new commit.

The Main Thread Is Not Yours — Den Odell

Every millisecond you spend executing JavaScript is a millisecond the browser can’t spend responding to a click, updating a scroll position, or acknowledging that the user did just try to type something. When your code runs long, you’re not causing “jank” in some abstract technical sense; you’re ignoring someone who’s trying to talk to you.

This is a great way to think about client-side JavaScript!

Also:

Before your application code runs a single line, your framework has already spent some of the user’s main thread budget on initialization, hydration, and virtual DOM reconciliation.

NoLoJS: Reducing the JS Workload with HTML and CSS - Web Performance Calendar

You might not need (much) JavaScript for these common interface patterns.

While we all love the power and flexibility JS provides, we should also respect it, and our users, by limiting its use to only what it needs to do.

Yes! Client-side JavaScript should do what only client-side JavaScript can do.

CSS-in-JS: The Great Betrayal of Frontend Sanity - The New Stack

This is a spot-on analysis of how CSS-in-JS failed to deliver on any of its promises:

CSS-in-JS was born out of good intentions — modularity, predictability and componentization. But what we got was complexity disguised as progress.

Escape Velocity: Break Free from Framework Gravity — Den Odell

React is no longer just a library. It’s a full ecosystem that defines how frontend developers are allowed to think.

Real talk!

Browsers now ship View Transitions, Container Queries, and smarter scheduling primitives. The platform keeps evolving at a fair pace, but most teams won’t touch these capabilities until React officially wraps them in a hook or they show up in Next.js docs.

Innovation keeps happening right across the ecosystem, but for many it only becomes “real” once React validates the approach. Which is fine, assuming you enjoy waiting for permission to use the platform you’re already building on.

Zing!

The critique isn’t that React is bad, but that treating any single framework as infrastructure creates blind spots in how we think and build. When React becomes the lens through which we see the web, we stop noticing what the platform itself can already do, and we stop reaching for native solutions because we’re waiting for the framework-approved version to show up first.

If your team’s evolution depends on a single framework’s roadmap, you are not steering your product; you are waiting for permission to move.

This isn’t a rhetorical question. I genuinely want to know why developers choose to build websites using React.

There are many possible reasons. Alas, none of them relate directly to user experience, other than a trickle-down justification: happy productive developers will make better websites. Citation needed.

It’s also worth mentioning that some people don’t choose to use React, but its use is mandated by their workplace (like some other more recent technologies I could mention). By my definition, this makes React enterprise software in this situation. My definition of enterprise software is any software that you use but that you yourself didn’t choose.

Inertia

By far the most common reason for choosing React today is inertia. If it’s what you’re comfortable with, you’d need a really compelling reason not to use it. That’s generally the reason behind usage mandates too. If we “standardise” on React, then it’ll make hiring more straightforward (though the reality isn’t quite so simple, as the React ecosystem has mutated and bifurcated over time).

And you know what? Inertia is a perfectly valid reason to choose a technology. If time is of the essence, and you know it’s going to take you time to learn a new technology, it makes sense to stick with what you know, even if it’s out of date. This isn’t just true of React, it’s true of any tech stack.

This would all be absolutely fine if React weren’t a framework that gets executed in browsers. Any client-side framework is a tax on the end user. They have to download, parse, and execute the framework in order for you to benefit.

But maybe React doesn’t need to run in the browser at all. That’s the promise of server-side rendering.

The front end

There used to be a fairly clear distinction between front-end development and back-end development. The front end consisted of HTML, CSS, and client-side JavaScript. The back end was anything you wanted as long as it could spit out those bits of the front end: PHP, Ruby, Python, or even just a plain web server with static files.

Then it became possible to write JavaScript on the back end. Great! Now you didn’t need to context-switch when you were scripting for the client or the server. But this blessing also turned out to be a bit of a curse.

When you’re writing code for the back end, some things matter more than others. File size, for example, isn’t really a concern. Your code can get really long and it probably won’t slow down the execution. And if it does, you can always buy your way out of the problem by getting a more powerful server.

On the front end, your code should have different priorities. File size matters, especially with JavaScript. The code won’t be executed on your server. It’s executed on all sorts of devices on all sorts of networks running all sorts of browsers. If things get slow, you can’t buy your way out of the problem because you can’t buy every single one of your users a new device and a new network plan.

Now that JavaScript can run on the server as well as the client, it’s tempting to just treat the code the same. It’s the same language after all. But the context really matters. Some JavaScript that’s perfectly fine to run on the server can be a resource hog on the client.

And this is where it gets interesting with React. Because most of the things people like about React still apply on the back end.

React developers

When React first appeared, it was touted as front-end tool. State management and a near-magical virtual DOM were the main selling points.

Over time, that’s changed. The claimed speed benefits of the virtual DOM turned out to be just plain false. That just left state management.

But by that time, the selling points had changed. The component-based architecture turned out to be really popular. Developers liked JSX. A lot. Once you got used to it, it was a neat way to encapsulate little bits of functionality into building blocks that can be combined in all sorts of ways.

For the longest time, I didn’t realise this had happened. I was still thinking of React as being a framework like jQuery. But React is a framework like Rails or Django. As a developer, it’s where you do all your work. Heck, it’s pretty much your identity.

But whereas Rails or Django run on the back end, React runs on the front end …except when it doesn’t.

JavaScript can run on the server, which means React can run on the server. It’s entirely possible to have your React cake and eat it. You can write all of your code in React without serving up a single line of React to your users.

That’s true in theory. The devil is in the tooling.

Priorities

Next.js allows you to write in React and do server-side rendering. But it really, really wants to output React to the client as well.

By default, you get the dreaded hydration pattern—do all the computing on the server in JavaScript (yay!), serve up HTML straight away (yay! yay!) …and then serve up all the same JavaScript that’s on the server anyway (ya—wait, what?).

It’s possible to get Next.js to skip that last step, but it’s not easy. You’ll be battling it every step of the way.

Astro takes a very different approach. It will do everything it can to keep the client-side JavaScript to a minimum. Developers get to keep their beloved JSX authoring environment without penalising users.

Alas, the collective inertia of the “modern” development community is bound up in the React/Next/Vercel ecosystem. That’s a shame, because Astro shows us that it doesn’t have to be this way.

Switching away from using React on the front end doesn’t mean you have to switch away from using React on the back end.

Why use React?

The titular question I asked is too broad and naïve. There are plenty of reasons to use React, just as there are plenty of reasons to use Wordpress, Eleventy, or any other technology that works on the back end. If it’s what you like or what you’re comfortable with, that’s reason enough.

All I really care about is the front end. I’m not going to pass judgment on anyone’s choice of server-side framework, as long as it doesn’t impact what you can do in the client. Like Harry says:

…if you’re going to use one, I shouldn’t be able to smell it.

Here’s the question I should be asking:

Why use React in the browser?

Because if the reason you’re using React is cultural—the whole team works in JSX, it makes hiring easier—then there’s probably no need to make your users download React.

If you’re making a single-page app, then …well, the first thing you should do is ask yourself if it really needs to be a single-page app. They should be the exception, not the default. But if you’re determined to make a single-page app, then I can see why state management becomes very important.

In that situation, try shipping Preact instead of React. As a developer, you’ll almost certainly notice no difference, but your users will appreciate the refreshing lack of bloat.

Mostly though, I’d encourage you to investigate what you can do with vanilla JavaScript in the browser. I totally get why you’d want to hold on to React as an authoring environment, but don’t let your framework limit what you can do on the front end. If you use React on the client, you’re not doing your users any favours.

You can continue to write in React. You can continue to use JSX. You can continue to hire React developers. But keep it on your machine. For your users, make the most of what web browsers can do.

Once you keep React on the server, then a whole world of possibilities opens up on the client. Web browsers have become incredibly powerful in what they offer you. Don’t let React-on-the-client hold you back.

And if you want to know more about what web browsers are capable of today, come to Web Day Out in Brighton on Thursday, 12th March 2026.

I Built the Same App 10 Times: Evaluating Frameworks for Mobile Performance | Loren Stewart

A very, very deep dive into like-for-like comparison of JavaScript frameworks. The takeaway:

Nuxt demonstrates that established “big three” frameworks can achieve next-gen performance when properly configured. Vue’s architecture allows competitive mobile web performance while maintaining a mature ecosystem. React and Angular show no path to similar results.

And the real takeaway:

Mobile is the web. These measurements matter because mobile web is the primary internet for billions of people. If your app is accessible via URL, people will use it on phones with cellular connections. Optimizing for desktop and hoping mobile is good enough is backwards. The web is mobile. Build for that reality.

Is it Time to Regulate React? – David Bushell – Web Dev (UK)

React exists as a profound perversion of the web platform. React has failed upwards to widespread adoption because it provides a “developer experience” that bypasses the hard parts. Like learning HTML, or CSS, or JavaScript. Even learning React itself is discouraged; that’s for adults, you should use meta-frameworks. React devs are burdened with multi-megabyte monstrosities before they’ve written a single line of code. You cannot fix “too much JavaScript” with more JavaScript and yet React devs are trained to npm install until their problems become their users’ problems.

Write Code That Runs in the Browser, or Write Code the Browser Runs - Jim Nielsen’s Blog

So instead of asking yourself, “How can I write code that does what I want?” Consider asking yourself, “Can I write code that ties together things the browser already does to accomplish what I want (or close enough to it)?”

V7: Video Killed the Web Browser Star | Rob Weychert

Grrr… it turns out that browsers exhibit some very frustrating behaviour when it comes to the video element. Rob has the details…

The present and potential future of progressive image rendering - JakeArchibald.com

When I set about writing this article, I intended it to be a strong argument for progressive rendering. But after digging into it, my feelings are less certain.

Tim recently gave a talk at Smashing Conference in New York called One Step Ahead. Based on the slides, it looks like it was an excellent talk.

Towards the end, there’s a slide that could be the tagline for Web Day Out:

Betting on the browser is our best chance at long-term success.

Most of the talk focuses on two technologies that you can add to any website with just a couple of lines of code: view transitions and speculation rules.

I’m using both of them on The Session and I can testify to their superpowers—super-snappy navigations with smooth animations.

Honestly, that takes care of 95% of the reasons for building a single-page app (the other 5% would be around managing state, which most sites—e-commerce, publishing, whatever—don’t need to bother with). Instead build a good ol’-fashioned website with pages of HTML linked together, then apply view transitions and speculation rules.

I mean, why wouldn’t you do that?

That’s not a rhetorical question. I’m genuinely interested in the reasons why people would reject a simple declarative solution in favour of the complexity of doing everything with a big JavaScript framework.

One reason might be browser support. After all, both view transitions and speculation rules are designed to be used as progressive enhancements, regardless of how many browsers happen to support them right now. If you want to attempt to have complete control, I understand why you might reach for the single-page app model, even if it means bloating the initial payload.

But think about that mindset for a second. Rather than reward the browsers that support modern features, you would instead be punishing them. You’d be treating every browser the same. Instead of taking advantage of the amazing features that some browsers have, you’d rather act as though they’re no different to legacy browsers.

I kind of understand the thinking behind that. You assume a level playing field by treating every browser as though they’re Internet Explorer. But what a waste! You ship tons of uneccesary code to perfectly capable browsers.

That could be the tagline for React.

I was going to save this announcement for later, but I’m just too excited: Harry Roberts will be speaking at Web Day Out!

Goddamn, that’s one fine line-up, and it isn’t even complete yet! Get your ticket if you haven’t already.

There’s a bit of a story behind the talk that Harry is going to give…

Earlier this year, Harry posted a most excellent screed in which he said:

The web as a platform is a safe bet. It’s un-versioned by design. That’s the commitment the web makes to you—take advantage of it.

• Opt into web platform features incrementally;
• Embrace progressive enhancement to build fast, reliable applications that adapt to your customers’ context;
• Write code that leans into the browser, not away from it.

Yes! Exactly!

Thing is, Harry posted this on LinkedIn. My indieweb sensibilities were affronted. So I harangued him:

You should blog this, Harry

My pestering paid off with an excellent blog post on Harry’s own site called Build for the Web, Build on the Web, Build with the Web:

The beauty of opting into web platform features as they become available is that your site becomes contextual. The same codebase adapts into its environment, playing to its strengths, rather than trying to build and ship your own environment from the ground up. Meet your users where they are.

That’s a pretty neat summation of the agenda for Web Day Out. So I thought, “Hmm …if I was able to pester Harry to turn a LinkedIn post into a really good blog post, I wonder if I could pester him to turn that blog post into a talk?”

I threw down the gauntlet. Harry accepted the challenge.

I’m sure you’re already familiar with Harry’s excellent work, but if you’re not, he’s basically Mr. Web Performance. That’s why I’m so excited to have him speak at Web Day Out—I want to hear the business case for leaning into what web browsers can do today, and he is most certainly the best person to bring receipts.

You won’t want to miss this, so be sure to get your ticket now; it’s only £225+VAT.

If you’re not ready to commit just yet, but you want to hear about more speaker announcements like this, you can sign up to the mailing list.

When I was talking about monitoring web performance yesterday, I linked to the CrUX data for The Session.

CrUX is a contraction of Chrome User Experience Report. CrUX just sounds better than CEAR.

It’s data gathered from actual Chrome users worldwide. It can be handy as part of a balanced performance-monitoring diet, but it’s always worth remembering that it only shows a subset of your users; those on Chrome.

The actual CrUX data is imprisoned in some hellish Google interface so some kindly people have put more humane interfaces on it. I like Calibre’s CrUX tool as well as Treo’s.

What’s nice is that you can look at the numbers for any reasonably popular website, not just your own. Lest I get too smug about the performance metrics for The Session, I can compare them to the numbers for WikiPedia or the BBC. Both of those sites are made by people who prioritise speed, and it shows.

If you scroll down to the numbers on navigation types, you’ll see something interesting. Across the board, whether it’s The Session, Wikipedia, or the BBC, the BFcache—back/forward cache—is used around 16% to 17% of the time. This is when users use the back button (or forward button).

Unless you do something to stop them, browsers will make sure that those navigations are super speedy. You might inadvertently be sabotaging the BFcache if you’re sending a Cache-Control: no-store header or if you’re using an unload event handler in JavaScript.

I guess it’s unsurprising the BFcache numbers are relatively consistent across three different websites. People are people, whatever website they’re browsing.

• The Session
• WikiPedia
• The BBC

Where it gets interesting is in the differences. Take a look at pre-rendering. It’s 4% for the BBC and just 0.4% for Wikipedia. But on The Session it’s a whopping 35%!

That’s because I’m using speculation rules. They’re quite straightforward to implement and they pair beautifully with full-page view transitions for a slick, speedy user experience.

It doesn’t look like WikiPedia or the BBC are using speculation rules at all, which kind of surprises me.

Then again, because they’re a hidden technology I can understand why they’d slip through the cracks.

On any web project, I think it’s worth having a checklist of The Invisibles—things that aren’t displayed directly in the browser, but that can make a big difference to the user experience.

Some examples:

• A web application manifest JSON file to help people install your website.
• A service worker, even if it’s just to cache static assets.
• Open Graph meta elements in the head of documents so they “unroll” nicely when the link is shared.
• An appropriate content security policy header.
• A Speculation-Rules header that points to a JSON file.
• An OpenSearch XML file if your site has search functionality.
• An icon, or as us olds call it, a favicon.
• A lang attribute on the body of every page.

If you’ve got a checklist like that in place, you can at least ask “Whose job is this?” All too often, these things are missing because there’s no clarity on whose responsible for them. They’re sorta back-end and sorta front-end.