File extension

.otf

OpenType font format

.otf files are OpenType fonts: scalable font files that may contain either PostScript-style (CFF) or TrueType outlines together with advanced typographic layout tables.

Known meanings

Formats and reference material for .otf

OpenType font format

Scalable font format with CFF or TrueType outlines and advanced layout features

  • fonts
  • Microsoft / Adobe
Open link

Details

Format notes

OpenType (OTF)

OpenType is a scalable font format developed by Microsoft and Adobe as a successor to TrueType and PostScript Type 1 fonts. It has since been standardized as ISO/IEC 14496-22 (Open Font Format). The .otf extension is conventionally used when the font contains PostScript-flavored CFF outlines, while TrueType-flavored OpenType fonts often keep the .ttf extension.

Structure

OpenType uses the sfnt wrapper: a table directory followed by tables that hold the data. The first four bytes identify the outline type: OTTO for CFF or CFF2 outlines, or 00 01 00 00 for TrueType outlines. Common tables include cmap (character to glyph mapping), head, hhea, hmtx, name, OS/2, and CFF (or glyf/loca for TrueType outlines). Layout tables such as GSUB, GPOS, and GDEF provide ligatures, kerning, and script-specific shaping. Variable fonts add tables such as fvar and gvar. A font collection uses the .ttc or .otc extension.

Adoption

OpenType is the standard desktop and web font format, supported by operating systems, browsers, and design software. The media type is font/otf. For web delivery, fonts are usually repackaged as WOFF or WOFF2.

Preservation And Security Notes

Preserve the original font file together with its license, since embedding and redistribution rights are recorded in the OS/2 and name tables and are governed by the license. Font parsers handle complex binary structures and have a history of vulnerabilities, so untrusted fonts should be processed by patched, sandboxed libraries.

Further Reading

  • OpenType specification (Microsoft): https://learn.microsoft.com/en-us/typography/opentype/spec/
  • OpenType font file organization: https://learn.microsoft.com/en-us/typography/opentype/spec/otff