Font Features Skill for Claude

Font Features (OpenType → CSS)

Inspect a font's real OpenType feature inventory and generate CSS to enable chosen features. Never guess what a font supports — always run scripts/otfeat.py list first; only features present in the dump may be offered or enabled.

Requires fontTools (pip install fonttools if missing).

Workflow

• Inspect the actual font files in the project:

   python3 <skill-dir>/scripts/otfeat.py list path/to/Font-Regular.woff2 [more fonts...]

Output lists each font's GSUB/GPOS tags with human descriptions (Monaspace stylistic sets are described precisely; unknown cvXX are labelled generically).

• Interview the user via cenno (mcp__cenno__ask_user, or ask_sequence for several questions). Offer ONLY features found in step 1, grouped sensibly, with a recommendation. Typical question set:
• Coding ligatures: which sets? (arrows ss03, colons ss07, comparison ss02...) — for code samples only, usually off for prose
• Numerals: tabular (tnum) for tables/timers, oldstyle (onum) for prose, slashed zero (zero)
• Texture healing (calt) — for Monaspace, recommend ON everywhere
• Caps: case for uppercase labels/buttons, smcp if present

Use input: {kind: "choice"} with a text option, mark optional questions low-urgency, and respect a "skip" answer.

• Generate CSS deterministically:

   python3 <skill-dir>/scripts/otfeat.py css --family "Monaspace Neon" \
     --features calt,liga,tnum,case --class prose
   # cvXX with a value: --features cv01=2

High-level font-variant-* properties are preferred automatically (they cascade and combine better); remaining tags fall back to font-feature-settings. --no-variant-props forces the low-level form only.

• Apply: paste the block into the project stylesheet; scope per element role (e.g. tnum on tables/stat tiles only, ligature sets on code only). Verify in a browser with real content.

Gotchas

• font-feature-settings is all-or-nothing per declaration — a second declaration on a nested element REPLACES the inherited list; repeat the full list. This is the main reason to prefer font-variant-*.
• CSS accepts any tag, browsers silently ignore ones the font lacks — which is why step 1 is mandatory (e.g. Monaspace has NO tnum/zero/smcp; it's a monospace family and zero is already slashed).
• Stylistic-set meanings are font-specific; never reuse Monaspace's ss-descriptions for another family.
• A feature tag being present does not mean it covers the glyphs assumed: dump the actual GSUB substitutions before writing demo copy (e.g. Monaspace's case only raises : ¡ ¿ ‽ and combining accents — NOT quotes, brackets, or dashes).
• Texture healing needs calt AND ligatures left enabled; font-variant-ligatures: none kills it.