Things not available when someone blocks all cookies

The other day, I received a harmless-looking Issue for my app SVGcode (announcement blog post). The Issue read:

Crash when opened with cookies blocked

Hey I block cookies by default. Unfortunately your website doesn’t handle that nicely despite it not needing (IMO) cookies to operate. I'm getting this error, because blocking cookies also blocks localStorage.

Uncaught DOMException: Failed to read the 'localStorage' property from 'Window': Access is denied for this document. Please add fallback to js provided localStorage, because it makes the app unusable.

I don't use cookies in the app at all, but for sure, when I disabled cookies in Chrome, the app wasn't usable.

Chrome Settings with all cookies blocked.

All I am using is some innocent localStorage and IndexedDB to persist user settings like the values of the sliders or the chosen color scheme.

Turns out, with all cookies blocked, Chrome disables a lot of (all?) APIs that can be used to persist data and thus potentially profile users. Here are the ones that I found:

The code sample below shows all these APIs and the error messages they throw when you try to use them with cookies blocked.

// Uncaught DOMException: Failed to read the 'localStorage' property from Window: Access is denied for this document.

// Uncaught DOMException: Failed to read the 'sessionStorage' property from 'Window: Access is denied for this document.

// Uncaught DOMException: An attempt was made to break through the security policy of the user agent.

const openRequest ='test', 1);
openRequest.onerror = function () {
// DOMException: The user denied permission to access the database.

openDatabase('test', '1', 'test', 1);
// Uncaught DOMException: An attempt was made to break through the security policy of the user agent.

await navigator.serviceWorker.register('.');
// Uncaught DOMException: Failed to register a ServiceWorker for scope ('') with script (''): The user denied permission to use Service Worker.

// Uncaught DOMException: Storage directory access is denied.

() => {},
(err) => console.error(err)
// DOMException: An ongoing operation was aborted, typically with a call to abort().

() => {},
(err) => console.error(err)
// DOMException: An ongoing operation was aborted, typically with a call to abort().

Did I miss anything? If so, please let me know!

Console errors when trying to access localStorage, sessionStorage, the Cache API, IndexedDB, and Web SQL.

The fix for the Issue was annoying, but simple. Always try...catch any potentially blocked calls:

SVGcode app with blocked cookies working and showing caught exceptions in the DevTools console.

Please report any other errors you encounter (I don't care for the analytics script failing). And thanks, @JakubekWeg for caring enough to having opened this Issue! Jakub is the proof that users exist who block any and all cookies. Check your error logs, you might be losing users, too!

(On a tangent, MDN is completely broken with cookies blocked, too. I was about to report this problem (because I care and love MDN 😍), when I discovered a PR is already under way that fixes the Issue. Thanks, @bershanskiy!)

MDN with blocked cookies

Thomas Steiner
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Announcing the Project Fugu API Showcase

One of the most frequent questions we hear on the Project Fugu team is: 🤔 "What are some of the apps people build with Project Fugu 🐡 APIs?"

The Project Fugu API Showcase is our answer:

Project Fugu API Showcase

It allows interested parties to get a filterable list of all the apps, big and small, that use a given API.

Need to prove that we're building obscure-sounding APIs like the Web Serial API for a reason? Select the API's chip and there goes a list of all the apps that use it:

Project Fugu API Showcase filtered on apps that use the Web Serial API

The Project Fugu API Showcase is community-driven. Everyone can submit apps for inclusion, and they will get listed after a short period of time of verification and approval.

Of course the Project Fugu API Showcase is contained in itself (yay, recursion 🎉), which means on supporting browsers you can use it to share it (or any other of the contained apps) with your followers:

Project Fugu API Showcase Project Fugu API Showcase and the iOS Share Sheet Project Fugu API Showcase and the Twitter compose tweet dialog

Please help spread the word and use this in discussions with the people you work with (whose apps you—or they—are obviously most welcome to add to the showcase):

Thomas Steiner
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iOS Browser Engine Choice

I'm following the (Twitter) conversation on browser engines other than WebKit to be allowed on iOS very closely. When the United Kingdom's Competition and Markets Authority (CMA) solicited responses from Web developers to their mobile ecosystems market study interim report, I sent one where I spoke as the developer of SVGcode and told the CMA about my experience with making the app performantly available on iOS Safari:

To whom it may concern,

I'm an employee of Google Germany, but also a hobbyist Web developer. Recently, I have built an application, SVGcode (, which I wanted to be performing well on all browsers, so I have put a lot of time and effort into making it as compatible and progressively enhanced as I could. Unfortunately, Safari is the one browser that constantly requires the most hoops to get to the same baseline experience as on other browsers like Firefox, Edge, or Chrome.

For example, it does not offer proper installation support, so rather than use my built-in Install button, I need to hope my users are aware of the hidden away "Add to Home Screen" feature in Safari.

Another missing feature is OffscreenCanvas, which would greatly improve the app's performance, but as is, the performance on Safari leaves to be desired. On macOS, I can just tell users that I have made the maximum effort to be compatible with all browsers, but if people wish to get the maximum performance, they are free to switch their browser to a one with the maximum amount of features supported.

On iOS and iPadOS, however, there is nothing I could tell my users, since even alternative browsers have to use WebKit's rendering engine under the hood. I do hope your legislation can help improve upon the situation and lift Apple's browser ban.

Respectfully yours,
Thomas Steiner

P.S. While I am employed by Google, I am speaking in a personal capacity for my work as a hobbyist developer outside of Google.

More impactful and lawyer-approved than mine are the responses from Mozilla and Google, though, which I invite you to read in their entirety. Below just two significant quotes:

Without regulatory intervention we believe there will be no change to the status quo, harming competition in browser engines and browsers, and harming innovation online.—Mozilla

Competition between browser engines—and freedom of choice for developers—means browser apps on Android can differentiate themselves by incorporating a range of features and functionalities that are not available on iOS, where all browsers are required to use Apple's WebKit browser engine.—Google

(It goes without saying but restating again: While I am employed by Google, I am speaking in a personal capacity for my work as a hobbyist developer outside of Google.)

Thomas Steiner
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Releasing SVGcode

Just a quick note to say that I have released SVGcode, a Progressive Web App that lets you convert raster images like JPG, PNG, GIF, WebP, AVIF, etc. to vector graphics in SVG format. You can find the source code on GitHub.

SVGcode app screenshot.

To learn more about the features of the app, read my article SVGcode: a PWA to convert raster images to SVG vector graphics or watch the video that is also embedded below.

SVGcode is starting to get some coverage, for example, from XDA Developers and even a Chinese website called 软餐. To help discoverability, I have also listed it on Stefan Judis' collection of Tiny Helpers. With the orange site it is always give and take, but for now (🤞), Hacker News treats the app quite well. Looking forward to seeing where the app goes.

Thomas Steiner
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Things mode and strings mode in Google Trends

Google Trends has essentially two modes:

A colleague of mine fell for this and was looking at the landing page for Progressive Web Apps in strings mode and was confused. The page the colleague should have looked at is the landing page for Progressive Web Apps in things mode. Its URL is

You can recognize things mode by looking at the q query parameter in the URL. If it starts with %2Fg%2F (URL-decoded: /g/), you are in things mode. The funny code 11bzxympx6 after that is the Knowledge Graph identifier. When you search for "11bzxympx6" on Google, you end up with exactly one search result that points to the Wikidata page for Progressive Web Apps. If you know the Knowledge Graph ID of something, you can hand-craft a URL that points people at exactly the right semantic search result on Google: See the bold Knowledge Graph ID at the end of the URL.

Google Trends showing "strings" and "things" mode side by side.

Note how Google Trends in the screenshot above even helpfully points out that…

[t]his comparison contains both Search terms and Topics, which are measured differently.

…and directs the reader to a help resource to learn more about the difference.

I happen to know all this because this is what I did my PhD in, and I have a paper at the ACM that describes the process we used for migrating our proprietary Knowledge Graph predecessor Freebase to the community-maintained Wikidata.

It's rare that I get to tell anyone about this stuff, so now you know more than you probably wanted to ever hear about this… You can learn more about this time of my Google life in my previous blog post. My manager back in the days didn't care about any of this, but maybe it's at least interesting to you… :-)

Thomas Steiner
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14 years at Google

Yesterday marked my 14 year Googleversary. I joined Google full time on October 1, 2007 as a new-grad straight from university. While for the Googleversary stats all that counts is full time employment, I was with Google way earlier. First as an intern between my second and third year at university starting on February 1, 2005, and then continuously throughout the rest of my studies as a temporary worker and via other internship contracts. The way this actual employment age shows is through the employee ID. Mine is in the 9,000 range, but people who joined about the time when I joined full-time have a 50,000 range ID. At the time of writing, 98.08871% of full time employees and extended workers have been at Alphabet for less time than me. During these 14 years, I've had 15 managers, some of them multiple times. I have 2.85-ified my salary (sounds impressive maybe, but I simply started very low), and have gone through three promotions. That's one promotion less than I think I could have had, but instead I enjoyed a different perk: I did my PhD on company time.

The PhD time (2010–2014) 🔗

While I wanted to do a PhD after three years on the job, I wasn't initially planning on doing it on company time. Quite the opposite. From February 1, 2010, I had reduced my work load to 60% to work on my PhD in the remaining 40%. After having this arrangement for two or three months, one evening my at the time manager's manager called to make me an offer I couldn't resist: to come back full time and work on I-SEARCH (A unIfied framework for multimodal content SEARCH), a three-year European project funded under FP7-ICT. This very manager left the company a couple of months later and his successor didn't see the same value in EU projects than the manager who left, and while they let me continue my (multi-year) work, my previous (Strongly) Exceeds ratings that I received for several quarters went down to regular Meets Expectations. Lesson learned in hindsight:

Never make your personal work arrangement depend on the goodwill of a sole manager, as powerful as this manager may appear.

During this time, I cranked out a number of publications (some of them fine, some of them mediocre), but above all made great friends and traveled the world. You can see me co-present the result of the project, a multimodal search engine, and to my surprise the user interface of I-SEARCH is still up.

My internship time (2005–2006) 🔗

My internship project—that sort of just evolved—was the Google AdWords PHP client library APIlity. At the time, the AdWords API (a very enterprise SOAP API) was brand new, and I happened to be the intern who was able to make it work. I had some experience with REST APIs from my Master's thesis, you can enjoy my first ever tech talk on the topic below.

The first few years (2007–2010) 🔗

During my first few full time years, I continued my work on the AdWords API as a Customer Solutions Engineer, but my heart always was with developer advocacy. I took on any opportunity I could get to hack my job and work with developers. One of my best memories is the 2008 series of Google Developer Days, where we toured all of Europe. Embedded below a presentation of mine on the Google Web Toolkit. An advantage of the early years was that Google was a lot smaller and job roles that were distinct in the US were still not present in Europe, so others like me who were just somewhat technical enough needed to jump in and represent locally.

After the PhD (2014–2018) 🔗

After finishing my PhD, I was (very naively so) disappointed that no one at the company cared. No pay raise. No job offer. I actually had to beg to go back to my previous Customer Solutions Engineer job that was the reason why I had started the PhD in the first place. While I tried for a while to get hired elsewhere and also switch jobs internally, nothing really worked out for various reasons (mostly location constraints and failed interviews). Another lesson learned:

Don't assume anyone in the company will care for your self-arranged further education. Having a PhD or not makes a difference as a new hire, but not later.

Getting into Chrome Developer Relations (2018) 🔗

Location always was a big factor in what roles you could get at Google. I made no secret of my interest in developer advocacy, but not being in one of the hub engineering offices meant this door was closed. I lobbied Paul Kinlan long enough until he eventually let me apply for a role on the Chrome Developer Relations team. The time between the interviews and the (thankfully positive) decision of the hiring committee was one of the most nerve-wrecking in my life. Long story short, it took me more than ten years to get the job I actually wanted. Not a real lesson, but more a reflection:

Taking an educated risk and doing what you really want while doing just enough to not get fired for doing too little of the things you actually get paid for is a strategy that sometimes works out. I wouldn't recommend it, unless you really, really want something.

Reflections on the present (2018–present) 🔗

Now I'm in Chrome Developer Relations since May 28, 2018 and it's an honestly great team to be on. My work is about evolving the Web and making things possible on the platform that were unthinkable before. I spoke twice at Google I/O, was part of Chrome Dev Summits, and presented at more international conferences than I can remember.

Ironically the corona crisis demonstrated that location didn't matter that much after all, at least for a distributed team like Chrome Developer Relations. Had corona come a couple of years ago, maybe they would have let me apply for the Developer Relations team way earlier, who knows. Since I started working for Google, I always lived a ten minute walk away from the office, but despite this short distance and even if I enjoy working in an office, I've now successfully applied for my position to be permanently remote. Mostly to secure the right.

What's next? 🔗

Is it time for the next gig? Maybe. It's very unusual for people in IT to stay on the same job for as long as I did. Will I see 15 years at Google? Who knows. Very probably so. For now, I'm definitely still having fun, at least most of the days. Have I become more cynical? Definitely. Do I panic when yet another re-org is being announced? Nope. One thing is certain, though: my heart still beats for the Web. Reach out if you have questions on anything that I wrote or if you want to discuss ideas. My DMs are open and my email is right on my About page.

Thomas Steiner
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Public statement of support for Annalena Baerbock and die Grünen for #BTW21

It's not often that I post something with the Political tag on my blog. In the recent months and probably years, I've in the majority sticked to Technical posts, but this one is different. For folks like me in tech, it's way too easy to limit oneself to just the mostly uncontroversial (as in: it truly matters) technical stuff and stay silent about other aspects of life. Yesterday, I watched the Triell (the TV debate between the three candidates for the German chancellor, Armin Laschet, Olaf Scholz, and Annalena Baerbock) and I took this as an excuse to make my political standpoint public. It's uncomfortable and I hesitated a lot, but I think it's the right thing™ to do now.

As Annalena Baerbock from the Grünen party says: "The next government is the last one that can still actively influence the climate crisis." You may have heard of the 2021 floodings in Germany. Our response can't be to rebuild and move on. If we continue the laissez faire of the German car industry that Mr. Laschet, the candidate of the Christian Democratic Party CDU, demands, we mainly get electric (or worse, hybrid) SUVs for 50K€+, but not affordable small cars for regular incomes. We don't need a Merkel 2.0 that Mr. Scholz risks to become with a little bit of CO₂ pricing here and a little bit of exit from coal energy there.

We need a politics where "[o]ur children, our grandchildren shouldn't have to ask us: Why didn't you do anything? But: How did you do it?"Annalena Baerbock.

If you're not super familiar with the current German political pre-election situation, here's some recommended background reading:

If you want to join me in going public with your political views, here's how I did it. It may feel uncomfortable, "cost" you followers or subscribers to your blog, or maybe even stop people from talking to you (I hope we keep talking, even if we don't agree with each other), but I think it's worth it.

Thomas Steiner
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Dark Mode Web App Manifest App Icons

I was asked if one could use SVG web app manifest app icons that are reactive to prefers-color-scheme. To illustrate what this means, here is an excerpt of a manifest where I set the icon to an SVG that is reactive to the color scheme. You can play with it by navigating directly to icon.svg and toggling your operating system's color scheme setting.

"icons": [{
"src": "",
"sizes": "144x144",
"type": "image/svg+xml"

The icon itself is just an SVG with embedded CSS. You may remember it from my post prefers-color-scheme in SVG favicons for dark mode icons.

(Side remark about a little gotcha: Note how I need to "lie" about the icon's dimensions in the web app manifest, where I say it's 144x144 pixels compared to the width and height in the source code.)

<svg width="100" height="100" xmlns="">
circle {
fill: yellow;
stroke: black;
stroke-width: 3px;
@media (prefers-color-scheme: dark) {
circle {
fill: black;
stroke: yellow;
<circle cx="50" cy="50" r="47"/>

So, to close this, the answer to the above question is yes, app icons will respect your preferred color scheme, but no, app icons won't update dynamically when you change your color scheme. Instead, they will keep their initial dark or light mode look from whatever you had your system set to at install time.

macOS Settings shows the system is set to light mode, but the app icon is still presented in dark mode, since it was installed when dark mode was enabled.

You can test it for yourself by installing the app embedded below (launch it in its own window).

(Credits: The app is a remix of Alexey Rodionov's app Alexey, you guessed it, is also the one who asked me about this.)

Thomas Steiner
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Excalidraw and Project Fugu 🐡 at Google I/O

Google I/O 2020, like all the I/O conferences before, was planned as a physical event. But then the coronavirus struck, and I/O 2020 was the I/O that never was. In 2021, we had enough time to plan, so I/O 2021 was the first virtual event in the series.

The team outdid themselves and recreated the entire experience as a virtual game. As Ars Technica wrote, Google's I/O Adventure was almost as good as being there. To get a feel for it, here's the official teaser video. During the event, you could bump into Googlers and talk to them, almost like in the real world. Below, you can see a team photo we took at the obligatory lighthouse. Can you spot me?

Google I/O Adventure team photo.

Together with @lipis, I had the pleasure of giving a talk titled Excalidraw and Fugu: Improving Core User Journeys. You can watch the talk in the video embed below, or read my video write-up over on

I also created a codelab that covers a lot of the Project Fugu 🐡 APIs. You can work your way through it at your own pace, or if you want, re-join me in a virtual workshop session where you see me do it—and run into some minor service worker caching issues… 😅

Google I/O 2021 was in my opinion a good event that worked OK enough under the circumstances and with the constraints of the virtual format. With I/O in the books, we're looking what to do when it comes to events in the future. Virtual, physical, or hybrid? The planning phase for Chrome Dev Summit 2021 has already started… Stay tuned, and always root for Team Web!

Thomas Steiner
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<ruby> HTML footnotes

It is sometimes surprising to me to see what kind of use cases HTML has a dedicated element for. Something that comes to mind is <output>, a container element into which a site or app can inject the results of a calculation or the outcome of a user action. For another use case that is arguably more common and which is also the topic of this blog post, HTML has nothing specific to offer: footnotesFootnotes are notes at the foot of the page while endnotes are collected under a separate heading at the end of a chapter, volume, or entire work. Unlike footnotes, endnotes have the advantage of not affecting the layout of the main text, but may cause inconvenience to readers who have to move back and forth between the main text and the endnotes..

Footnotes in HTML, then and now

Despite several proposals to deal with footnotes at the language level, HTML 3.0 Draft was the last version of HTML that offered the FN element. It was designed for footnotes, and when practical, footnotes were to be rendered as pop-up notes. You were supposed to use the element as in the code sample below (the inconsistent character casing sic).

You should not have believed me, for virtue cannot so
<a href="#fn1">inoculate</a> our old stock but we shall
<a href="#fn2">relish of it</a>. I loved you not.

<DD>I was the more deceived.</DD>

Get thee to a nunnery. Why wouldst thou be a breeder of sinners? I am myself
<a href="#fn2">indifferent honest</a> ...

<fn id="fn1"><i>inoculate</i> - graft</fn>
<fn id="fn2"><i>relish of it</i> - smack of it (our old sinful nature)</fn>
<fn id="fn3"><i>indifferent honest</i> - moderately virtuous</fn>

The current HTML Living Standard (snapshot from January 22, 2021) remarks that HTML does not have a dedicated mechanism for marking up footnotes and recommends the following options for footnotes. For short inline annotations, the title attribute could be used.

<p><b>Customer</b>: Hello! I wish to register a complaint. Hello. Miss?</p>
<span title="Colloquial pronunciation of 'What do you'">Watcha</span> mean,

<b>Customer</b>: Uh, I'm sorry, I have a cold. I wish to make a complaint.
<b>Shopkeeper</b>: Sorry,
<span title="This is, of course, a lie.">we're closing for lunch</span>.

Using title comes with an important downside, though, as the spec rightly notes.

Unfortunately, relying on the title attribute is currently discouraged as many user agents do not expose the attribute in an accessible manner as required by this specification (e.g. requiring a pointing device such as a mouse to cause a tooltip to appear, which excludes keyboard-only users and touch-only users, such as anyone with a modern phone or tablet).

For longer annotations, the a element should be used, pointing to an element later in the document. The convention is that the contents of the link be a number in square brackets.

<p>Announcer: Number 16: The <i>hand</i>.</p>
Interviewer: Good evening. I have with me in the studio tonight Mr Norman St
John Polevaulter, who for the past few years has been contradicting people. Mr
Polevaulter, why <em>do</em> you contradict people?

Norman: I don't. <sup><a href="#fn1" id="r1">[1]</a></sup>
<p>Interviewer: You told me you did! ...</p>

<p id="fn1">
<a href="#r1">[1]</a> This is, naturally, a lie, but paradoxically if it
were true he could not say so without contradicting the interviewer and thus
making it false.

This approach is what most folks use today, for example, Alex Russell or the HTML export of Google Docs documents.

The ruby element

The other day, I came across a tweet by Michael Scharnagl, whose website and Twitter handle are aptly named Just Markup and who runs a Twitter campaign this year called #HTMLElementInATweet:

Day 22: <ruby>

Represents small annotations

ℹ️ The term ruby originated as a unit of measurement used by typesetters, representing the smallest size that text can be printed on newsprint while remaining legible.…


— Michael Scharnagl (@justmarkup) January 22, 2021

I had heard about ruby in the past, but it was one of these elements that I tend to look up and forget immediately. This time, for some reason, I looked closer and even consulted the spec.

The ruby element allows one or more spans of phrasing content to be marked with ruby annotations. Ruby annotations are short runs of text presented alongside base text, primarily used in East Asian typography as a guide for pronunciation or to include other annotations. In Japanese, this form of typography is also known as furigana.

The rt element marks the ruby text component of a ruby annotation. When it is the child of a ruby element, it doesn't represent anything itself, but the ruby element uses it as part of determining what it represents.

You are supposed to use it like so.

<ruby> 明日 <rp>(</rp><rt>Ashita</rt><rp>)</rp> </ruby>

The MDN docs describe the ruby element as follows.

The HTML <ruby> element represents small annotations that are rendered above, below, or next to base text, usually used for showing the pronunciation of East Asian characters. It can also be used for annotating other kinds of text, but this usage is less common.

The term ruby originated as a unit of measurement used by typesetters, representing the smallest size that text can be printed on newsprint while remaining legible.

Hmm 🤔, this sounds like it could fit the footnotes use case. So I went and tried my luck in creating ruby HTML footnotes.

Using ruby for footnotes

The markup is straightforward, all you need are ruby for the footnote, and rt for the footnote text. I like that the footnote is just part of the flow text, so I do not need to mentally switch context when writing. I also do not have to manually number my footnotes and come up with and remember the value of ids. Another small advantage is that footnotes are not part of copied text, so when you copy content from my site, you do not end up with "text [2] like this". The snippet below shows the markup of a footnote.

<body tabindex="0">
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec consectetur
dictum fermentum. Vivamus non fringilla dolor, in scelerisque massa. Quisque
mattis elit quam, eu hendrerit diam ultricies ut. Nunc sit amet velit
posuere, malesuada diam in, congue diam. Integer quis venenatis velit. Donec
quis nunc
<ruby tabindex="0"
vel purus<rt
Lorem ipsum dolor sit amet, consectetur adipiscing elit.

maximus dictum. Sed nec tempus odio. Vestibulum et lobortis ante. Duis
blandit pulvinar lectus non sollicitudin. Nulla non imperdiet diam. Fusce
varius ultricies sapien id pretium. Praesent ut pellentesque massa. Nunc eu
tellus hendrerit risus maximus porta. Maecenas in molestie erat.

The CSS to make the automatic footnote numbering work is based on a CSS counter. The rt is styled in a way that it is not displayed by default, and only gets shown when the ruby's :after, which holds the footnote number, is focused. For this to function properly, it is important to make the <ruby> element focusable by setting tabindex="0". On mobile devices, the body needs to be focusable as well, so the footnote can be closed again by clicking/tapping anywhere in the page. The rt element can contain phrasing content, so links and images are all fine. Another thing to remember is to make sure the rt element remains visible on :hover, so links can be clicked even when the ruby element loses focus. I have moved the CSS display value of rt into a CSS custom property, so I could easily play with different values. The CSS below is all it takes to make the footnotes work.

/* Behavior */

/* Set up the footnote counter and display style. */
body {
counter-reset: footnotes;

/* Make footnote text appear as `inline-block`. */
ruby {
--footnote-display: inline-block;

/* Display the actual footnote [1]. */
ruby:after {
counter-increment: footnotes;
/* The footnote is separated with a thin space. 🤓 */
content: ' [' counter(footnotes) ']';

/* Remove the focus ring. */
ruby:focus {
outline: none;

/* Display the footnote text. */
ruby:focus rt {
display: var(--footnote-display);

/* Hide footnote text by default. */
rt {
display: none;

* Make sure the footnote text remains visible,
* so contained links can be clicked.

rt:hover {
display: var(--footnote-display);

The following CSS snippet determines the look and feel of the footnotes.

/* Look and feel */

/* Footnote text styling. */
rt {
background-color: #eee;
color: #111;
padding: 0.2rem;
margin: 0.2rem;
max-width: 30ch;

/* Images in footnote text styling. */
rt img {
width: 100%;
height: auto;
display: block;

/* Footnote styling */
ruby:after {
color: red;
cursor: pointer;
font-size: 0.75rem;
vertical-align: top;

Something I could not get to work (yet) is to make the rt's CSS position to be absolute. I got the best results so far by making the rt an inline block by setting the CSS property --footnote-display: inline-block. I am well aware of ruby-align and ruby-position. The former does not have great browser support at the moment but seems relevant, and the latter seems to have no effect when I change the display value of rt to anything other than the UA stylesheet default, which is block. If you manage to get it to work such that footnote texts open inline, floating right under the footnote and not affecting the surrounding paragraph text, your help would be very welcome. I also still need to look into supporting printable footnotes. If you are interested, you can reach me and discuss this idea on Twitter.


I have enabled ruby footnotes right on my blog This is the second footnote, the other is at the top., but you can also play with a standalone demo on Glitch and remix its source code.

⚠️ Please note that this is not production ready. Support seems decent on Blink/WebKit-based browsers, but not so great on Gecko-based browsers like Firefox. I have opened an Issue with the CSS Working Group to hear their opinion on the idea.

Other approaches

The "standards nerd and technology enthusiast" Terence Eden proposed to use details in a blog post titled A (terrible?) way to do footnotes in HTML. Next, Peter-Paul Koch, web developer, consultant, and trainer, runs a side project named The Thidrekssaga and footnotes where for the current iteration of the site he just notes that his "implementation of footnotes is mostly shit". If you have yet another approach apart from what is listed here and above, please reach out and I am happy to add it. And as I wrote before, I am looking for help from CSS experts to make rt positioned absolutely. Sorry for the nerd-snipe.

Thomas Steiner
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