[SquareWheel]

Thanks for the link. I've actually used this one before, but it's not quite what I was hoping for.

These settings (font-size, line-height) are defined in the content CSS, not the @font-face rule, so they won't be automatically applied when the font is swapped. Properties like size-adjust or ascent-override are better for matching like-fonts as it's all automatic.

Also, while it is very useful to have a tool to come up with your own pairings, I think a list that covers some of the most popular fonts and creates perfect settings would be very useful for quick implementations. Something like the submitted site above that has done the legwork for you.

[corny]

Maybe this is more what you're looking for? https://screenspan.net/fallback

[SquareWheel]

Much closer to what I had in mind! Thanks, this one is new to me. It would've saved me time in my previous testing.

Hopefully one day the existing CSS properties like letter-spacing can be supported in @font-face to allow for even better matching. That would make techniques like this even more powerful.