Katex in mdbook

book.toml

[book]
authors = ["Remco Bloemen"]
language = "en"
multilingual = false
src = "src"

[build]
create-missing = false

[preprocessor.html]
command = "python3 html.py"
renderer = ["html"]

html.py

#!/usr/bin/env python3
import json
import sys

if len(sys.argv) > 1:
    if sys.argv[1] == 'supports':
        # sys.argv[2] is the renderer name
        sys.exit(0)

html = '\n' + open('katex-header.html', 'r').read()
context, book = json.load(sys.stdin)

def fix(items):
    for section in items:
        if 'Chapter' in section:
            section['Chapter']['content'] += html
            fix(section['Chapter']['sub_items'])

fix(book['sections'])
json.dump(book, sys.stdout)

katex-header.html

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/katex.min.css"
    integrity="sha384-zB1R0rpPzHqg7Kpt0Aljp8JPLqbXI3bhnPWROx27a9N0Ll6ZP/+DiW/UqRcLbRjq" crossorigin="anonymous">
<script defer src="https://cdn.jsdelivr.net/npm/[email protected]/dist/katex.min.js"
    integrity="sha384-y23I5Q6l+B6vatafAwxRu/0oK/79VlbSz7Q9aiSZUvyWYIYsd+qj+o24G5ZU2zJz"
    crossorigin="anonymous"></script>
<script defer src="https://cdn.jsdelivr.net/npm/[email protected]/dist/contrib/auto-render.min.js"
    integrity="sha384-kWPLUVMOks5AQFrykwIup5lo0m3iMkkHrD0uJ4H5cjeGihAutqP0yW0J6dpFiVkI"
    crossorigin="anonymous"></script>
<script>
    document.addEventListener("DOMContentLoaded", function () {
        renderMathInElement(document.body, {
            fleqn: false,
            macros: {
                "\\F": "\\mathbb{F}",
                "\\O": "\\mathcal{O}",
                "\\(": "\\left(",
                "\\)": "\\right)",
                "\\norm": "\\left\\vert #1 \\right\\vert",
                "\\set": "\\mathcal{ #1 }",
                "\\floor": "\\left\\lfloor{ #1 }\\right\\rfloor",
                "\\ceil": "\\left\\lceil{ #1 }\\right\\rceil",
                "\\mod": "\\left\\[{ #1 }\\right\\]",
            },
            delimiters: [
                { left: "$$", right: "$$", display: true },
                { left: "\\(", right: "\\)", display: false },
                { left: "$", right: "$", display: false },
                { left: "\\[", right: "\\]", display: true }
            ]
        });
    });
</script>