How to find out which OpenType font features are supported by a font on Linux

Recently, I had an .otf font file, and I wanted to find out which OpenType font feature tags (such as tnum for fixed-width or tabular numbers, or liga for ligatures) it supports. These are used, for example, in the font-feature-settings CSS property. [My actual use case was that I wanted to use font features in my Waybar configuration.]

The supported font features can be listed with the otfinfo command, like so

otfinfo --features path/to/font/file.otf
For example, for Inter, it shows 
$ otfinfo --features /usr/share/fonts/rsms-inter-fonts/Inter-Regular.ttf
aalt    Access All Alternates
c2sc    Small Capitals From Capitals
calt    Contextual Alternates
case    Case-Sensitive Forms
ccmp    Glyph Composition/Decomposition
cpsp    Capital Spacing
cv01    Character Variants 1
cv02    Character Variants 2
cv03    Character Variants 3
cv04    Character Variants 4
cv05    Character Variants 5
cv06    Character Variants 6
cv07    <unknown feature>
cv08    <unknown feature>
cv09    <unknown feature>
cv10    <unknown feature>
cv11    <unknown feature>
cv12    <unknown feature>
cv13    <unknown feature>
dlig    Discretionary Ligatures
dnom    Denominators
frac    Fractions
kern    Kerning
mark    Mark Positioning
mkmk    Mark to Mark Positioning
numr    Numerators
ordn    Ordinals
pnum    Proportional Figures
salt    Stylistic Alternates
sinf    Scientific Inferiors
smcp    Small Capitals
ss01    Stylistic Set 1
ss02    Stylistic Set 2
ss03    Stylistic Set 3
ss04    Stylistic Set 4
ss05    Stylistic Set 5
ss06    Stylistic Set 6
ss07    Stylistic Set 7
ss08    Stylistic Set 8
subs    Subscript
sups    Superscript
tnum    Tabular Figures
zero    Slashed Zero

On my system (Fedora 40), the otfinfo command was already installed. Not sure if it’s there by default or if it came as a dependency of something else.

As an additional quick tip, you can use the command fc-list <font name> to find out the font file(s) for a given font. For me, it shows the following for Inter: 
$ fc-list Inter
/usr/share/fonts/rsms-inter-fonts/Inter-Light.ttf: Inter,Inter Light:style=Light,Regular
/usr/share/fonts/rsms-inter-fonts/Inter-Thin.ttf: Inter,Inter Thin:style=Thin,Regular
/usr/share/fonts/rsms-inter-fonts/Inter-Black.ttf: Inter,Inter Black:style=Black,Regular
/usr/share/fonts/rsms-inter-fonts/Inter-BoldItalic.ttf: Inter:style=Bold Italic
/usr/share/fonts/rsms-inter-fonts/Inter-ExtraLight.ttf: Inter,Inter ExtraLight:style=ExtraLight,Regular
/usr/share/fonts/rsms-inter-fonts/Inter-ThinItalic.ttf: Inter,Inter Thin:style=Thin Italic,Italic
/usr/share/fonts/rsms-inter-fonts/Inter-ExtraBold.ttf: Inter,Inter ExtraBold:style=ExtraBold,Regular
/usr/share/fonts/rsms-inter-fonts/Inter-Medium.ttf: Inter,Inter Medium:style=Medium,Regular
/usr/share/fonts/rsms-inter-fonts/Inter-ExtraLightItalic.ttf: Inter,Inter ExtraLight:style=ExtraLight Italic,Italic
/usr/share/fonts/rsms-inter-fonts/Inter-BlackItalic.ttf: Inter,Inter Black:style=Black Italic,Italic
/usr/share/fonts/rsms-inter-fonts/Inter-LightItalic.ttf: Inter,Inter Light:style=Light Italic,Italic
/usr/share/fonts/rsms-inter-fonts/Inter-Italic.ttf: Inter:style=Italic
/usr/share/fonts/rsms-inter-fonts/Inter-SemiBoldItalic.ttf: Inter,Inter SemiBold:style=SemiBold Italic,Italic
/usr/share/fonts/rsms-inter-fonts/Inter-Regular.ttf: Inter:style=Regular
/usr/share/fonts/rsms-inter-fonts/Inter-ExtraBoldItalic.ttf: Inter,Inter ExtraBold:style=ExtraBold Italic,Italic
/usr/share/fonts/rsms-inter-fonts/Inter-Bold.ttf: Inter:style=Bold
/usr/share/fonts/rsms-inter-fonts/Inter-MediumItalic.ttf: Inter,Inter Medium:style=Medium Italic,Italic
/usr/share/fonts/rsms-inter-fonts/Inter-SemiBold.ttf: Inter,Inter SemiBold:style=SemiBold,Regular

You can also use the fc-match command to find out the file for the best matching font for a CSS font-family style query:

$ fc-match --format "%{file}\n" Inter
/usr/share/fonts/rsms-inter-fonts/Inter-Regular.ttf

$ fc-match --format "%{file}\n" sans-serif
/usr/share/fonts/google-noto-vf/NotoSans[wght].ttf

$ fc-match --format "%{file}\n" monospace
/usr/share/fonts/google-noto-vf/NotoSansMono[wght].ttf

If you leave out the --format or -f option, you get some additional info, but not the full file path:

$ fc-match Inter
Inter-Regular.ttf: "Inter" "Regular"

That’s all!

The otfinfo command was surprisingly hard to find. I tried several search engines for queries like “linux find out opentype font features” or “linux find out font tabular numbers”, but I could only find results like these:

This struggle compelled me to write this post in the spirit of Simon Willison’s TIL page. I hope you found it useful.

Some further reading: