Getting the Most Out of Variable Fonts on Google Fonts

I have spent the past several years working (alongside a bunch of super talented people) on a font family called Recursive Sans & Mono, and it just launched officially on Google Fonts!

Wanna try it out super fast? Here’s the embed code to use the full Recursive variable font family from Google Fonts (but you will get a lot more flexibility & performance if you read further!)

<link href="https://fonts.googleapis.com/css2?family=Recursive:slnt,wght,CASL,CRSV,[email protected],300..1000,0..1,0..1,0..1&display=swap" rel="stylesheet">

I started Recursive as a thesis project for a type design masters program at KABK TypeMedia, and when I launched my type foundry, Arrow Type, I was subsequently commissioned by Google Fonts to finish and release Recursive as an open-source, OFL font.

You can see Recursive and learn more about it what it can do at recursive.design. 

Recursive is made to be a flexible type family for both websites and code, where its main purpose is to give developers and designers some fun & useful type to play with, combining fresh aesthetics with the latest in font tech.

First, a necessary definition: variable fonts are font files that fit a range of styles inside one file, usually in a way that allows the font user to select a style from a fluid range of styles. These stylistic ranges are called variable axes, and can be parameters, like font weight, font width, optical size, font slant, or more creative things. In the case of Recursive, you can control the “Monospacedness” (from Mono to Sans) and “Casualness” (between a normal, linear style and a brushy, casual style). Each type family may have one or more of its own axes and, like many features of type, variable axes are another design consideration for font designers.

You may have seen that Google Fonts has started adding variable fonts to its vast collection. You may have read about some of the awesome things variable fonts can do. But, you may not realize that many of the variable fonts coming to Google Fonts (including Recursive) have a lot more stylistic range than you can get from the default Google Fonts front end.

Because Google Fonts has a huge range of users — many of them new to web development — it is understandable that they’re keeping things simple by only showing the “weight” axis for variable fonts. But, for fonts like Recursive, this simplification actually leaves out a bunch of options. On the Recursive page, Google Fonts shows visitors eight styles, plus one axis. However, Recursive actually has 64 preset styles (also called named instances), and a total of five variable axes you can adjust (which account for a slew of more potential custom styles).

Recursive can be divided into what I think of as one of four “subfamilies.” The part shown by Google Fonts is the simplest, proportional (sans-serif) version. The four Recursive subfamilies each have a range of weights, plus Italics, and can be categorized as:

• Sans Linear: A proportional, “normal”-looking sans-serif font. This is what gets shown on the Google Fonts website.
• Sans Casual: A proportional “brush casual” font
• Mono Linear: A monospace “normal” font
• Mono Casual: A monospace “brush casual” font

This is probably better to visualize than to describe in words. Here are two tables (one for Sans, the other for Mono) showing the 64 named instances:

But again, the main Google Fonts interface only provides access to eight of those styles, plus the Weight axis:

Not many variable fonts today have more than a Weight axis, so this is an understandable UX choice in some sense. Still, I hope they add a little more flexibility in the future. As a font designer & type fan, seeing the current weight-only approach feels more like an artificial flattening than true simplification — sort of like if Google Maps were to “simplify” maps by excluding every road that wasn’t a highway.

Luckily, you can still access the full potential of variable fonts hosted by Google Fonts: meet the Google Fonts CSS API, version 2. Let’s take a look at how you can use this to get more out of Recursive.

But first, it is helpful to know a few things about how variable fonts work.

How variable fonts work, and why it matters

If you’ve ever worked with photos on the web then you know that you should never serve a 9,000-pixel JPEG file when a smaller version will do. Usually, you can shrink a photo down using compression to save bandwidth when users download it.

There are similar considerations for font files. You can often reduce the size of a font dramatically by subsetting the characters included in it (a bit like cropping pixels to just leave the area you need). You can further compress the file by converting it into a WOFF2 file (which is a bit like running a raster image file though an optimizer tool like imageOptim). Vendors that host fonts, like Google Fonts, will often do these things for you automatically.

Now, think of a video file. If you only need to show the first 10 seconds of a 60-second video, you could trim the last 50 seconds to have a much small video file. 

Variable fonts are a bit like video files: they have one or more ranges of information (variable axes), and those can often either be trimmed down or “pinned” to a certain location, which helps to reduce file size. 

Of course, variable fonts are nothing like video files. Fonts record each letter shape in vectors, (similar to how SVGs store shape information). Variable fonts have multiple “source locations” which are like keyframes in an animation. To go between styles, the control points that make up letters are mathematically interpolated between their different source locations (also called deltas). A font may have many sets of deltas (at least one per variable axis, but sometimes more). To trim a variable font, then, you must trim out unneeded deltas.

As a specific example, the Casual axis in Recursive takes letterforms from “Linear” to “Casual” by interpolating vector control points between two extremes: basically, a normal drawing and a brushy drawing. The ampersand glyph animation below shows the mechanics in action: control points draw rounded corners at one extreme and shift to squared corners on the other end.

Generally, each added axis doubles the number of drawings that must exist to make a variable font work. Sometimes the number is more or less – Recursive’s Weight axis requires 3 locations (tripling the number of drawings), while its Cursive axis doesn’t require extra locations at all, but actually just activates different alternate glyphs that already exist at each location. But, the general math is: if you can cut unneeded axes from a variable font, you will usually get a smaller file.

When using the Google Fonts API, you are actually opting in to each axis. This way, instead of starting with a big file and whittling it down, you get to pick and choose the parts you want.

Variable axis tags

If you’re going to use the Google Fonts API, you first need to know how to label axes. Every axis has both a full name and an abbreviation.

These axis abbreviations are in the form of four-letter “tags.” These are lowercase for axes defined by Microsoft and recorded in the OpenType spec, and uppercase for newer axes invented or defined by others (these are also called “custom” or “private” axes). There are efforts to standardize some of these new axes.

There are currently five standard axes a font can include: 

• wght – Weight, to control lightness and boldness
• wdth – Width, to control overall letter width
• opsz – Optical Size, to control adjustments to design for better readability at various sizes
• ital – Italic, generally to switch between separate upright/italic designs
• slnt – Slant, generally to control upright-to-slanted designs with intermediate values available

Custom axes can be almost anything. Recursive includes three of them — Monospace (MONO), Casual (CASL), and Cursive (CRSV)  — plus two standard axes, wght and slnt.

Google Fonts API basics

When you configure a font embed from the Google Fonts interface, it gives you a bit of HTML or CSS which includes a URL, and this ultimately calls in a CSS document that includes one or more @font-face rules. This includes things like font names as well as links to font files on Google servers.

This URL is actually a way of calling the Google Fonts API, and has a lot more power than you might realize. It has a few basic parts: 

1. The main URL, specifying the API (https://fonts.googleapis.com/css2)
2. Details about the fonts you are requesting in one or more family parameters
3. A font-display property for setting a display parameter

As an example, let’s say we want the regular weight of Recursive (in the Sans Linear subfamily). Here’s the URL we would use with our CSS @import:

@import url('https://fonts.googleapis.com/css2?family=Recursive&display=swap');

Or we can link it up in the <head> of our HTML:

<link href="https://fonts.googleapis.com/css2?family=Recursive&display=swap" rel="stylesheet">

Once that’s in place, we can start applying the font in CSS:

body {
  font-family: 'Recursive', sans-serif;
}

There is a default value for each axis:

• MONO 0 (Sans/proportional)
• CASL 0 (Linear/normal)
• wght 400 (Regular)
• slnt 0 (upright)
• CRSV 0 (Roman/non-cursive lowercase)

Choose your adventure: styles or axes

The Google Fonts API gives you two ways to request portions of variable fonts:

1. Listing axes and the specific non-default values you want from them
2. Listing axes and the ranges you want from them

Getting specific font styles

Font styles are requested by adding parameters to the Google Fonts URL. To keep the defaults on all axes but use get a Casual style, you could make the query Recursive:[email protected] (this will serve Recursive Sans Casual Regular). To make that Recursive Mono Casual Regular, specify two axes before the @ and then their respective values (but remember, custom axes have uppercase tags):

https://fonts.googleapis.com/css2?family=Recursive:CASL,[email protected],1&display=swap

To request both Regular and Bold, you would simply update the family call to Recursive:[email protected];700, adding the wght axis and specific values on it:

https://fonts.googleapis.com/css2?family=Recursive:[email protected];700&display=swap

A very helpful thing about Google Fonts is that you can request a bunch of individual styles from the API, and wherever possible, it will actually serve variable fonts that cover all of those requested styles, rather than separate font files for each style. This is true even when you are requesting specific locations, rather than variable axis ranges — if they can serve a smaller font file for your API request, they probably will.

As variable fonts can be trimmed more flexibility and efficiently in the future, the files served for given API requests will likely get smarter over time. So, for production sites, it may be best to request exactly the styles you need.

Where it gets interesting, however, is that you can also request variable axes. That allows you to retain a lot of design flexibility without changing your font requests every time you want to use a new style.

Getting a full variable font with the Google Fonts API

The Google Fonts API seeks to make fonts smaller by having users opt into only the styles and axes they want. But, to get the full benefits of variable fonts (more design flexibility in fewer files), you should use one or more axes. So, instead of requesting single styles with Recursive:[email protected];700, you can instead request that full range with Recursive:[email protected] (changing from the ; to .. to indicate a range), or even extending to the full Recursive weight range with Recursive:[email protected] (which adds very little file size, but a whole lot of extra design oomph).

You can add additional axes by listing them alphabetically (with lowercase standard axes first, then uppercase custom axes) before the @, then specifying their values or ranges after that in the same order. For instance, to add the MONO axis and the wght axis, you could use Recursive:wght,[email protected],0..1 as the font query.

Or, to get the full variable font, you could use the following URL:

https://fonts.googleapis.com/css2?family=Recursive:slnt,wght,CASL,CRSV,[email protected],300..1000,0..1,0..1,0..1&display=swap

Of course, you still need to put that into an HTML link, like this:

<link href="https://fonts.googleapis.com/css2?family=Recursive:slnt,wght,CASL,CRSV,[email protected],300..1000,0..1,0..1,0..1&display=swap" rel="stylesheet">

Customizing it further to balance flexibility and filesize

While it can be tempting to use every single axis of a variable font, it’s worth remembering that each additional axis adds to the overall files ize. So, if you really don’t expect to use an axis, it makes sense to leave it off. You can always add it later.

Let’s say you want Recursive’s Mono Casual styles in a range of weights, you could do:

<link href="https://fonts.googleapis.com/css2?family=Recursive:CASL,MONO,[email protected],1,300..1000&display=swap" rel="stylesheet">

The above doesn’t work anymore 🤷. Maybe it was a beta feature or maybe it’s just changed syntax. Feel free to contact us if you know more.

You can add multiple font families to an API call with additional family parameters. Just be sure that the fonts are alphabetized by family name.

<link href="https://fonts.googleapis.com/css2?family=Inter:slnt,[email protected],100..900?family=Recursive:CASL,MONO,[email protected],1,300..1000&display=swap" rel="stylesheet">

Using variable fonts

Standard axes can all be controlled with existing CSS properties. For instance, if you have a variable font with a weight range, you can specify a specific weight with font-weight: 425;. All axes can be controlled with font-variation-settings. So, if you want a Mono Casual very-heavy style of Recursive (assuming you have called the full family as shown above), you could use the following CSS:

body {
 font-weight: 950;
 font-variation-settings: 'MONO' 1, 'CASL' 1;
}

Something good to know: font-variation-settings is much nicer to use along with CSS custom properties. 

You can read more specifics about designing with variable fonts at VariableFonts.io and in the excellent collection of CSS-Tricks articles on variable fonts.

Nerdy notes on the performance of variable fonts

If you were to use all 64 preset styles of Recursive as separate WOFF2 files (with their full, non-subset character set), it would be total of about 6.4 MB. By contrast, you could have that much stylistic range (and everything in between) at just 537 KB in a variable font. Of course, that is a slightly absurd comparison — you would almost never actually use 64 styles on a single web page, especially not with their full character sets (and if you do, you should use subsets with unicode-range).

A better comparison is Recursive with one axis range versus styles within that axis range. In my testing, a Recursive WOFF2 file that’s subset to the “Google Fonts Latin Basic” character set (including only characters to cover English and Western European languages), including the full 300–1000 Weight range (and all other axes “pinned” to their default values) is 60 KB. Meanwhile, a single style with the same subset is 25 KB. So, if you use just three weights of Recursive, you can save about 15 KB by using the variable font instead of individual files.

The full variable font as a subset WOFF2 clocks in at 281 KB which is kind of a lot for a font, but not so much if you compare it to the weight of a big JPEG image. So, if you assume that individual styles are about 25 KB, if you plan to use more than 11 styles, you would be better off using the variable font.

This kind of math is mostly an academic exercise for two big reasons:

1. Variable fonts aren’t just about file size.The much bigger advantage is that they allow you to just design, picking the exact font weights (or other styles) that you want. Is a font looking a little too light? Bump up the font-weight a bit, say from 400 to 425!
2. More importantly (as explained earlier), if you request variable font styles or axes from Google Fonts, they take care of the heavy lifting for you, sending whatever fonts they deem the most performant and useful based on your API request and the browsers visitors access your site from.

So, you don’t really need to go downloading fonts that the Google Fonts API returns to compare their file sizes. Still, it’s worth understanding the general tradeoffs so you can best decide when to opt into the variable axes and when to limit yourself to a couple of styles.

What’s next?

Fire up CodePen and give the API a try! For CodePen, you will probably want to use the CSS @import syntax, like this in the CSS panel:

@import url('https://fonts.googleapis.com/css2?family=Recursive:CASL,CRSV,MONO,slnt,[email protected],0..1,0..1,-15..0,300..1000&display=swap');

It is apparently better to use the HTML link syntax to avoid blocking parallel downloads of other resources. In CodePen, you’d crack open the Pen settings, select HTML, then drop the <link> in the HTML head settings.

Or, hey, you can just fork my CodePen and experiment there:

Take an API configuration shortcut

If you are want to skip the complexity of figuring out exact API calls and looking to opt into variable axes of Recursive and make semi-advanced API calls, I have put together a simple configuration tool on the Recursive minisite (click the “Get Recursive” button). This allows you to quickly select pinned styles or variable ranges that you want to use, and even gives estimates for the resulting file size. But, this only exposes some of the API’s functionality, and you can get more specific if you want. It’s my attempt to get people using the most stylistic range in the smallest files, taking into account the current limitations of variable font instancing.

Use Recursive for code

Also, Recursive is actually designed first as a font to use for code. You can use it on CodePen via your account settings. Better yet, you can download and use the latest Recursive release from GitHub and set it up in any code editor.

Explore more fonts!

The Google Fonts API doc helpfully includes a (partial) list of variable fonts along with details on their available axis ranges. A couple of my favorites with axes beyond just Weight are Encode Sans (wdth, wght) and Inter (slnt, wght). You can also filter Google Fonts to show only variable fonts, though most of these results have only a Weight axis (still cool and useful, but don’t need custom URL configuration).

Some more amazing variable fonts are coming to Google Fonts. Some that I am especially looking forward to are:

• Fraunces: “A display, “Old Style” soft-serif typeface inspired by the mannerisms of early 20th century typefaces such as Windsor, Souvenir, and the Cooper Series”
• Roboto Flex: Like Roboto, but with an extensive ranges of Weight, Width, and Optical Size
• Crispy: A creative, angular, super-flexible variable display font
• Science Gothic: A squarish sans “based closely on Bank Gothic, a typeface from the early 1930s—but a lowercase, design axes, and language coverage have been added”
• Commissioner: A low-contrast humanist sans-serif with almost classical proportions with three “voices” with stems that can be straight, flaired, or wedged.

And yes, you can absolutely download and self-host these fonts if you want to use them in your projects today. But stay tuned to Google Fonts for more awesomely-flexible typefaces to come!

Of course, the world of type is much bigger than open-source fonts. There are a bunch of incredible type foundries working on exciting, boundary-pushing fonts, and many of them are also exploring new & exciting territory in variable fonts. Many tend to take other approaches to licensing, but for the right project, a good typeface can be an extremely good value (I’m obviously biased, but for a simple argument, just look at how much typography strengthens brands like Apple, Stripe, Google, IBM, Figma, Slack, and so many more). If you want to feast your eyes on more possibilities and you don’t already know these names, definitely check out DJR, OHno, Grilli, XYZ, Dinamo, Typotheque, Underware, Bold Monday, and the many very-fun WIP projects on Future Fonts. (I’ve left out a bunch of other amazing foundries, but each of these has done stuff I particularly love, and this isn’t a directory of type foundries.)

Finally, some shameless plugs for myself: if you’d like to support me and my work beyond Recursive, please consider checking out my WIP versatile sans-serif Name Sans, signing up for my (very) infrequent newsletter, and giving me a follow on Instagram.