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Castoro is a libre font family released under the SIL Open Font License. Castoro is a specific instance of an adaptive design developed for Tiro Typeworks’ internal use as a base from which to generate tailored Latin companions for some of our non-European script types. The instance that has been expanded to create the Castoro fonts was initially made for the Indic fonts that we produced for Harvard University Press. In the Castoro version, we have retained the extensive diacritic set for transliteration of South Asian languages, and added additional characters for an increased number of European languages.

The parent design here presented as the Castoro instance began as a synthesis of aspects of assorted Dutch types from the 16–18th Centuries. Castoro roman was designed by John Hudson, and the italic with his Tiro colleague Paul Hanslow, assisted by Kaja Słojewska. The extended Castoro collection consists of Castoro regular and italic text fonts, published in June 2020, and the all-caps Castoro Titling font, published in December 2020.

Why ‘Castoro’? One wants a typeface name to be easy to remember, and to be evocative of some association or characteristic of the design—poetic even. For our libre and open source projects, we have added the restrictive convention that the name must end in the letter –o. Castoro is named for the North American beaver, Castor canadensis. Robust serif text types with extensive language and typographic layout support are sometimes referred to as ‘workhorse’ types. Castoro may be thought of as a busy beaver.

The splendid beaver illustration that adorns this page and other Castoro materials is by Lucy Conklin, and is used with permission.


The canonical design sources for the Castoro project are the FontLab 7 .vfj files in the source folder. These sources contain all necessary aspects of the Castoro typefaces, including the OpenType Layout coding and kerning.

The .ufo build input sources are exported from FontLab 7 using the default UFO package profile.

These are the only sources necessary for the Castoro build.

Build process

14 December 2020

The Castoro fonts now use a new build process, based on the one that Tiro Typeworks also uses for its commercial library and client projects. The script uses a YAML configuration file to identify UFO build sources and version string (the YAML file may contain additional, optional parameters that are not used in the Castoro project).

The build script outputs TTF and CFF OpenType fonts, and WOFF and WOFF2 packaging of each (this is hard coded and not configurable). The sequence of operations is:

  • build TTF/OTF
  • remove overlaps
  • autohint (ttfautohint and AFDKO)
  • optimise
  • build WOFF/WOFF2


From the top level, Castoro folder:

# Create a new virtualenv
python3 -m venv venv
# Activate env
source venv/bin/activate
# Install dependencies
pip3 install -r requirements.txt

For subsequent use (presuming the requirements have not changed), only the second of those steps will be required.

Run the build script indicating the YAML configuration file (for separate build streams, use separate YAML files).

$ python tools/ castoro.yml


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