Inter Math

Math drawn from Inter, variable in weight (100–900) and optical size (14–32): an OpenType math font for what sets math (LaTeX, Typst, Word, MathML, MathJax), which KaTeX takes too, with the metrics KaTeX lays it out with and a switch back to Computer Modern.

Every symbol KaTeX documents is drawn from Inter: letters and digits, the operators and relations, the AMS symbols (with their own designs where they share a character with Main), the larger delimiters and big operators, blackboard bold, and sans serif (\mathsf, Inter being one). What Inter has no design for stays in KaTeX's fonts: typewriter, Fraktur, calligraphic and script letters, and ℜ ℑ ℘ ℵ ℶ ℷ ℸ.

TeX's layout follows the font too: fraction bars, rules and √ are as thick as Inter Math's minus sign at every weight, the math axis sits on its operators' centre, and underlines, strike-throughs and arrows are Inter's own.

Use it

The OpenType math font

One font with a MATH table, the standard way fonts carry math layout, for LaTeX (LuaLaTeX and XeLaTeX with unicode-math), Typst, Word, PowerPoint, LibreOffice and MathML in browsers. It is the same design as KaTeX's Inter Math, laid out by TeX's rules as Inter Math gives them to KaTeX: rules as thick as the minus sign at every weight, √ and delimiters growing a tenth of an em at a time and stacked past their largest, Unicode's math alphabets (italic, bold, sans serif, double-struck).

Each release's ZIP has it in opentype/: its nine weights (InterMath-Thin.ttf to InterMath-Black.ttf, the family "Inter Math"), which desktop apps take, and InterMathVariable.ttf. Install the weights, then:

\usepackage{unicode-math}
\setmathfont{Inter Math}

#show math.equation: set text(font: "Inter Math")

In Word and PowerPoint, pick it as the equations' font (Equation Options). For MathML (browsers' own math layout, Temml), the npm package has inter-math/mathml.css: its nine weights as web fonts, math taking the weight of its text.

For MathJax 4, the package has the same font as MathJax's (its svg.js: the SVG output, at the Regular weight), which MathJax loads from the package's URL, with a component that has no font of its own:

<script>
  window.MathJax = { output: { font: "https://cdn.jsdelivr.net/npm/inter-math" } };
</script>
<script defer src="https://cdn.jsdelivr.net/npm/mathjax@4/tex-svg-nofont.js"></script>

Its em is Inter's: math is as large as Inter's text at the same size. Script, Fraktur and monospace letters, which Inter has no design for, come from another math font (unicode-math's range option).

With KaTeX, from npm

pnpm add inter-math

The package brings its own KaTeX (0.19.0, with the hooks Inter Math lays math out through), its stylesheet and the fonts:

import "inter-math/katex.min.css"; // KaTeX's stylesheet and Inter Math's (katex.css unminified)
import katex from "inter-math/katex"; // KaTeX with Inter Math's hooks; its extensions at inter-math/katex/contrib/*
import { setMathFont } from "inter-math";

setMathFont("inter", { weight: 400 }); // "classic" restores KaTeX's own layout exactly
katex.render("e^{i\\pi} + 1 = 0", element);

Put the inter-math class on an ancestor of the math, and give the CSS the same weight (--inter-math-weight). KaTeX's settings are global: math already rendered keeps its layout until it is rendered again. withMathFont renders with one font and then restores the current one.

The stylesheet sets KaTeX's math in the OpenType math font (its variable font): each role KaTeX has a font for (upright, italic, AMS, blackboard, the four sizes of delimiters and big operators) is a feature of the font's own, in KaTeX's em.

The arrows drawn with small heads (AMS arrows such as ↣ ⇉ ↺ ↰, and the vectors \vec, \overrightarrow…) have angle heads, as every other arrow does. setMathFont("inter", { arrowHeads: "triangle" }) gives them filled triangles, like Inter's own small arrows (the font's ss01 stylistic set).

The package's own README (build/README.npm.md) says more: KaTeX's extensions, libraries that import katex themselves, a CDN.

The fonts

Each release has a ZIP: the OpenType math font (opentype/), the same font for MathJax (mathjax-font/), and the npm package (katex/: the KaTeX integration, the stylesheets for MathML, their fonts).

Develop

pnpm install       # KaTeX 0.19.0, with patches/katex@0.19.0.patch applied
pnpm font:setup    # once: the build's Python, with fontTools, in build/.venv
pnpm font:build    # the fonts, the OpenType math font, and the sources generated from them

Command	What it does
pnpm font:build	builds a font per role KaTeX sets math in from Inter (build/out/*.ttf) and writes the generated sources (src/metrics.ts, src/provenance.ts) and build/parts.md (what each glyph is built on, and what is built on it); then the OpenType math font from them (build/opentype.py: build/out/opentype/, fonts/InterMath-*.woff2, fonts/InterMathVariable.woff2), and MathJax's font from it (build/mathjax.py: src/mathjax-font/)
pnpm test	KaTeX's layout in both fonts: rules, surds, arrows, underlines, the switch back to KaTeX's fonts
pnpm typecheck	TypeScript
pnpm workbench	the test pages on http://localhost:3150
pnpm examples	the examples (examples/: KaTeX, MathML, Temml, TeXZilla, MathJax, from the package pnpm dist builds) on http://127.0.0.1:3153/examples/
pnpm dist	builds the deliverables into dist/ and checks them (build/deliver.mjs): the npm package (dist/npm/, its tarball) and the release ZIP
pnpm release	builds the fonts again, tests, typechecks, pnpm dist, then tags vX.Y.Z, publishes to npm and makes the GitHub release with the ZIP (--dry-run: npm's dry run, no tag)
node workbench/katex-docs.mjs	re-extracts the examples of KaTeX's documentation for the installed version (workbench/katex-docs.json)

The workbench pages have weight and size sliders and a white-on-black mode: school-math specimens with a box to try any LaTeX; every symbol and function in KaTeX's documentation in Computer Modern, in Inter Math, and in the Inter glyphs each one is drawn from (Inter's own glyphs in blue, the rest drawn for Inter Math); the package as pnpm dist builds it.

Linked from this repository (inter-math@link:), the package is src/: the app needs the same patched KaTeX through pnpm's patchedDependencies, and loads inter-math/inter-math.css after KaTeX's own stylesheet.

Path	What
sources/inter/	Inter's variable fonts, the source
build/	the build (Python and fontTools): build.py, one module per family of glyphs, patch_katex.py (KaTeX's hooks); the OpenType math font, opentype.py (its MATH table: math_table.py; its variants and pieces: math_glyphs.py); MathJax's font, mathjax.py; the delivery, deliver.mjs, and the package's README
src/	setMathFont, surds, KaTeX's SVG images redrawn, the CSS (KaTeX's, and MathML's: mathml.css), MathJax's font (mathjax-font/, generated), generated metrics and provenance
fonts/	the built WOFF2 files the CSS loads
patches/	KaTeX's patch, generated by build/patch_katex.py
test/	the vitest suite
workbench/	the test pages: plain HTML and ES modules, served by Vite
examples/	the examples: plain HTML, the package from dist/npm/

Release

package.json's version is the release's: the npm package's, the tag's (v1.0.0) and the fonts' (head.fontRevision and name ID 5, as Geist's: M.X.Y is M.(100X+Y), 1.0.0 is 1.000). To release:

1. raise the version in package.json and write its notes in CHANGELOG.md (## X.Y.Z);
2. pnpm font:build (the fonts carry the version), pnpm dist to check, and commit;
3. git tag vX.Y.Z && git push origin main vX.Y.Z.

The tag starts the release workflow: it builds the fonts again (they must come out as committed), tests, packs, stages the version on npm through trusted publishing, and makes the GitHub release with the ZIP and the changelog's notes. The version goes public on npm once approved with a maintainer's second factor:

npm stage list inter-math
npm stage approve <stage-id>

(or npmjs.com, the package's Staged Packages tab). pnpm release does the same from this machine (the first release, before npm trusted the workflow). Commits follow Conventional Commits.

Licence

The fonts are under the SIL Open Font License 1.1, as Inter's (OFL.txt), and so is the rest of this repository. The npm package also carries KaTeX, under the MIT licence, and KaTeX's own fonts, under the OFL (its LICENSE.md).