UFO (format)

UFO (format)
Name	UFO
Extension	.ufo
Mime	application/x-font
Owner	Silkan N. Foundry
Released	2012
Genre	Font file format

UFO (format)

UFO (Unified Font Object) is an open, XML-based file format for storing font source data. It provides a human-readable, tool-agnostic container used by type designers and software projects such as Adobe Systems, Google, Monotype Imaging, Linotype, and FontLab-related workflows. The format aims to standardize interchange among projects like RoboFont, Glyphs, FontForge, Keith Packard-led utilities, and build systems including FontTools and GlyphsApp-adjacent scripts.

Overview

UFO stores glyph outlines, metrics, kerning, guidelines, metadata, and lib entries in a directory structure using XML plist files and individual glyph files. Designers working with tools such as RoboFont, Glyphs, FontLab Studio, FontForge, and DTP pipelines benefit from interoperability between editors and build systems like fontmake, MutatorMath, Defcon, and ufoLib. The format is used in projects tied to type revivals, scholarly fonts in institutions like The British Library and Museum of Modern Art, and open font projects contributed via platforms such as GitHub, GitLab, and Bitbucket.

History and development

UFO originated from collaboration among type designers and developers influenced by projects like Adobe Type 1, TrueType, and open-source initiatives including FreeType and Mozilla font tooling. Early contributors included members of RoboFont and the Silicon Valley Type Foundry community; development accelerated through contributions from Tal Leming-affiliated projects, Silkan N. Foundry-linked engineers, and maintainers of FontTools and Defcon. Subsequent iterations were shaped by real-world needs from foundries such as Monotype Imaging and academic work at Stanford University and Massachusetts Institute of Technology typography labs. The format has been revised to address multi-master, variable font concepts introduced by OpenType variable axes and communities around Adobe, Google Fonts, and Apple Inc..

Technical specifications

UFO is a directory-based package comprising files like "fontinfo.plist", "metainfo.plist", "glyphs/*.glif", and "kerning.plist". Glyph outlines use the GLIF XML schema, which encodes cubic or quadratic Bézier contours compatible with converters targeting TrueType or OpenType outlines. Metadata fields reference standards and identifiers familiar to systems such as OpenType tables and registries used by W3C-related typography discussions. The format supports annotations including anchors, guides, and lib entries used by tools like MutatorMath for interpolation and fontmake for building final binaries. Unicode mappings conform to code point conventions maintained by Unicode Consortium registries and can include naming schemes used by Adobe Glyph List and foundry-specific conventions.

Implementations and software support

Implementations of UFO readers and writers exist in libraries and applications such as FontTools, defcon, ufoLib, RoboFont, GlyphsApp, FontForge, fontmake, and various plugin ecosystems for Sublime Text and Visual Studio Code extensions tailored to type design. Continuous integration pipelines on GitHub Actions and Travis CI commonly use FontTools-based tooling to validate and compile UFOs into binary fonts. Interoperability projects include converters between UFO and proprietary formats from FontLab and exporters integrated into design suites like Adobe Illustrator and Affinity Designer via intermediary scripts.

Usage and applications

UFO is primarily used as a source format during type design, variable font generation, and collaborative font production across teams at foundries such as Monotype Imaging and independent studios publishing to Google Fonts or selling via MyFonts and Fontspring. It underpins academic digitization efforts at institutions like The British Library and Harvard University and is used in digital restoration projects linked to archives at Bibliothèque nationale de France and Smithsonian Institution. Scripted workflows for hinting, interpolation, and testing leverage tools like MutatorMath, fontTools.varLib, and test suites used by Microsoft and Apple Inc. for platform compatibility checks.

Compatibility and file conversion

Because UFO stores source data, conversion pipelines translate UFO to binaries like OpenType (.otf/.ttf) or legacy TrueType fonts using build tools such as fontmake, fontTools, and foundry-owned compilers. Converters map GLIF cubic coordinates to quadratic outlines or outline decompositions compatible with Windows and macOS renderers and may incorporate autohinting using utilities influenced by FreeType algorithms. Migration between proprietary sources from FontLab or GlyphsApp and UFO often involves scripts maintained on GitHub or vendor exporters provided by the respective companies.

Criticisms and limitations

Critiques of UFO focus on fragmentation of extensions, inconsistent support across proprietary tools like GlyphsApp and FontLab, and lack of a single authoritative governance body akin to standards organizations such as IETF or ISO. Some foundries report challenges when dealing with complex OpenType features, variable font axis metadata, and binary-only data such as hint programs, which are not fully addressed by the base UFO schema. Community efforts hosted on platforms like GitHub and discussions involving organizations such as Adobe and Google continue to propose enhancements, but adoption varies among stakeholders including academic labs and commercial foundries.

Category:Font formats