.sfd File — SplineFontDB Font Source

SFD (Spline Font Database) is the native file format for FontForge, the leading free and open-source font editor. SFD files store complete font design data in a text-based format including glyph outlines (as cubic and quadratic splines), metrics (advance widths, side bearings, kerning pairs), hinting instructions, OpenType feature definitions, multiple master axes, bitmap strikes, metadata, and font-level properties. The text-based nature of SFD files makes them ideal for version control — font designers can track changes to individual glyphs, spacing adjustments, and feature updates through Git or other VCS systems. SFD files contain the full editable source of a font, from which compiled formats (OTF, TTF, WOFF, WOFF2) are generated. The format supports Unicode mapping for tens of thousands of glyphs, multiple lookup tables for complex script shaping, mark positioning for diacritics, and contextual alternates. Many open-source fonts are developed using FontForge with SFD sources published alongside compiled binaries. The format provides a complete, human-inspectable representation of font data that can be processed by scripts for automated font production workflows.