1. Never assume that a named font will work

There are no web-safe fonts; none are available across all major platforms.

Web fonts (@font-face and all) are not safe either:

• If not inlined, subresources can fail to load for all kinds of network reasons.
• Font loading is an area of concern for security, so some block it for safety.
• uBlock Origin has a dedicated button for disabling remote fonts.
• I think some browsers’ data-saving modes block fonts from loading.
  (And those that don’t, should.)

Or the user might have elected not to let websites choose their own fonts.

I’ve been doing that since 2020, and it makes the web so much better.

For me, generic families are the only ones that will work.

One related JS thing: if you ever use document.fonts.load("1em my-web-font"),
remember that it’s fallible: the promise it returns may be rejected.
I came across about four things in the six years 2020–2025 that broke for this reason
(and two of them were in 2025).

Now for a couple of consequence of this.

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pre {
	font-family: "jgs", monospace;
}

I was actually going to write that last point as “always include a generic family”,
but really it’s only monospace that it’s important for. Still—

font-family: Arial, sans-serif;

font-family: Times New Roman, serif;

2. Stop enumerating fonts that the system might have installed

I’ve seen too much of this kind of thing:

font-family: "Arial", Helvetica, 'Helvetica Neue', Liberation Sans, "Noto Sans", sans-serif;

Google Sans, Roboto, Arial, sans-serif

It doesn’t help. sans-serif will resolve to a font no worse than those you named, and quite possibly better.

Here’s a real example I just came across (with spaces restored after punctuation, for it was minified):

font-family: Menlo, Monaco, Lucida Console, Liberation Mono, DejaVu Sans Mono, Bitstream Vera Sans Mono, Courier New, monospace, serif

This is ridiculous, strictly worse than font-family: monospace, monospace. monospace will resolve to a font that is no worse.

Now I’m not saying there’s never a case for it.
Consider Georgia and Times New Roman, both serifs from Microsoft’s Core fonts for the Web.
But they have quite different character: Georgia is a good deal wider.
If that’s what you want for stylistic reasons, I will not begrudge you font-family: Georgia, serif.

3. Strongly consider using only a generic family

So perhaps we’ve removed the locally-installed fonts as not useful;
now how about web fonts?

A web font is slower than no web font; and you can run into issues loading them; so we got font-display.

But really, instead of messing around with block and swap periods and redrawing and reflowing tradeoffs,
why not just use whatever font the user has?

It won’t be that bad. They might even have chosen fonts themselves.

Consider it.

font-family: Menlo, Monaco, Lucida Console, Liberation Mono, DejaVu Sans Mono, Bitstream Vera Sans Mono, Courier New, monospace, serif

4. Don’t use system-ui or ui-* for content

UI fonts are designed for short UI texts, not longform content.

UI fonts may not support your content language well: macOS is good about it,
but Windows is not, and you’ll end up with things like CJK users getting a bad monospaced font.

Sometimes, people have even deliberately chosen ridiculous system UI font—
quite common in some Android circles.
I presume system-ui will make content look ridiculous too.

w3c/csswg-drafts issue #3658 discusses some of the problems,
concluding that system-ui has been extensively abused.
mdn/content issue #41244 finally added a note to MDN discouraging its overuse.

These families have largely been used as a proxy for better default fonts. This is not a good use of them.

I believe system-ui was a mistake.
They should have left it at -apple-system and had BlinkMacSystemFont change to that:
no other platform had a useful equivalent concept at the time (though some do now),
and it was evident from well before the time of standardisation that
almost all use of this stuff was abuse working around the fact that
browsers weren’t updating their poorly-considered, ancient defaults for the existing generic families.

I believe that ui-serif, ui-sans-serif, ui-monospace and especially ui-rounded was an entirely stupid idea which should still be ripped out.
Especially given that they’re not expected to map to any font on… anything non-Apple.
Being Apple-only, they don’t need to be in the spec.
They can just expose them as fonts with names that just happen to start with -apple-.

(What, we’re not doing prefixes any more? This isn’t a prefix, just looks like one.)