SyntaxFont

Build a font with built-in syntax highlighting from any base font — inspired by Font with Built-In Syntax Highlighting.

Highlighting lives entirely in OpenType (COLR/CPAL + calt). It works in <pre>, <code> and <textarea>, and themes switch at runtime from CSS.

Live app: https://inchei.github.io/SyntaxFont/

Quick start

uv sync
uv run syntaxfont build -f assets/JetBrainsMono-Regular.ttf -l js,css,html -t default -o dist

How it works

• Generation — src/syntaxfont/ duplicates glyphs as empty .altN alternates, paints them via COLR/CPAL, and injects generated calt rules with feaLib. The same code runs in the browser inside Pyodide (Web Worker, web/worker.js), so nothing is uploaded.
• Themes — the first selected theme is baked into CPAL; every selected theme is also emitted as CSS @font-palette-values for runtime switching.
• Languages — languages/*.yaml declares keywords, symbols and comment/string regions. Conflicting rules warn in the CLI and web UI; --isolated-languages emits one feature per language instead.

Command line

uv run syntaxfont build -f base.ttf -l js,python -t night --palettes default -o out

Option	Meaning
-f	base TTF/OTF/TTC/WOFF/WOFF2 font
--font-number	face index for TTC collections (default 0)
-l	comma-separated language names or YAML paths
-t	theme name or YAML path
-o	output directory
--palettes	extra themes emitted as @font-palette-values
--name-suffix	output filename suffix (default -highlight)
--emit-fea	also write the generated features.fea
--ascii-only	only color ASCII inside comments/strings (smaller output)
--extra-chars	extra characters to color inside comments/strings (e.g. ，。！)
--keep-ligatures	keep the base font's ligatures instead of dropping them
--isolated-languages	one OpenType feature per language instead of one combined calt

Known limitations

• Matching is literal and bounded: no regular expressions, newlines end every region, long names/interpolations may color partially.
• All enabled languages share one calt (conflicts warn; --isolated-languages avoids this).
• Ligatures are dropped by default; kept ligatures get a single color and can swallow later triggers (comment/string delimiters still win).
• Without --keep-ligatures, ccmp/locl/rlig are dropped, so complex-script shaping will not work.
• Not yet: regex literals, nested block comments, heredocs, multi-line strings, embedded grammars (HTML <script>, Markdown fences), semantic type-name coloring.

Development

uv run pytest
uv run python scripts/build_web.py      # bundle sources + configs into web/data
uv run python -m http.server -d web 8000  # serve over http, not file://

scripts/make_logo.py renders the logo; scripts/shiki_coverage.py measures highlighting coverage against Shiki (--badge refreshes assets/shiki-coverage.svg). CI runs tests and deploys web/ to GitHub Pages (see .github/workflows/pages.yml).

License

GPL-3.0-or-later — see LICENSE.