Everything you need to know about OTF
OTF (OpenType Font, .otf) is Adobe and Microsoft's joint successor to TrueType, finalized in 1996. It supports both TrueType outlines AND PostScript-style cubic Bezier curves (CFF), plus advanced typography features like ligatures, alternate glyphs, and contextual alternates. OTF is what professional typographers reach for.
How it works under the hood
- Two outline flavors. OTF can use TTF-style quadratic Beziers OR PostScript-style cubic Beziers (CFF/CFF2). The latter compresses better but renders slightly differently.
- Advanced typography (OpenType features). Ligatures (fi, fl), small caps, oldstyle figures, swashes - all controlled via OpenType features (`liga`, `smcp`, `onum`, `swsh`).
- Substitution and positioning tables. GSUB (glyph substitution) and GPOS (glyph positioning) tables enable complex script support - Arabic shaping, Indic conjuncts, kerning.
- Variable fonts. OTF and TTF both support OpenType v1.8 variable fonts since 2016 - one file with axes for weight, width, slant.
Where you'll actually use it
- Professional typography (Adobe InDesign, Affinity Publisher)
- Designer-focused web typography where features matter
- Print and book design (the typographic feature support justifies the file)
- Multi-script support (Arabic, Indic, CJK)
How it compares to alternatives
OTF vs TTF: OTF supports cubic Beziers and advanced features; TTF is simpler with quadratic Beziers. WOFF2 is what you actually serve on the web.
Things that will trip you up
- OTF advanced features need browser support - older Safari versions ignore some features
- CSS `font-feature-settings: 'liga'` enables ligatures, but it's all-or-nothing per feature
- Variable OTF fonts can be larger than static OTF - use static for small file size, variable for design flexibility
Test it yourself: FontForge (open-source editor), Glyphs (Mac), FontLab (cross-platform), `otfinfo` for inspection. Browser DevTools shows resolved features.