OTFeatureFreezer GUI app and pyftfeatfreeze commandline tool in Python to permanently "apply" OpenType features to fonts, by remapping their Unicode assignments

View the Project on GitHub twardoch/fonttools-opentype-feature-freezer

OpenType Feature Freezer

With OpenType Feature Freezer, you can “freeze” some OpenType features into a font.

These features are then “on by default”, so characters previously accessible through OpenType features only (such as smallcaps, oldstyle numerals or localized forms) will now be accessible even in apps that don’t support OpenType features, such as LibreOffice, OpenOffice, or in apps that don’t support a particular feature, such as Microsoft Office in case of smallcaps.

Note: This tool actually remaps the cmap table of the font by applying the specified GSUB features. It will not work for substitutions where neither glyph has any cmap entries. Only single and alternate substitutions are supported.

This tool comes in two versions: OTFeatureFreezer: a simple GUI (graphical) app for macOS and Windows that you can download and run without any special perparations, and pyftfeatfreeze: a CLI (command-line) app that required Python 3.6 or newer to be installed on your computer.

Current version: 1.32


Install the OTFeatureFreezer GUI app for macOS

Download DMG for macOS

  1. On macOS, click the Download link above.
  2. Ctrl+click the downloaded DMG, choose Open, then Open again.
  3. Drag the icon to your /Applications folder.
  4. When you run the app for the first time, Ctrl+click the, choose Open, then click Open.
  5. Later, you can just double-click the icon to run the app. If the app does not run, double-click again.
  6. See the Documentation for info about how to use the GUI app. The GUI corresponds to the command-line options.

Install the OTFeatureFreezer GUI app for Windows (64-bit)

Download ZIP for Windows

  1. You need a 64-bit version of Windows, 7 or newer. 32-bit Windows is not supported.
  2. Click the Download link above.
  3. Unzip the downloaded ZIP.
  4. Double-click the setup_featfreeze.exe icon to install the app.
  5. Run OTFeatureFreezer from your Start menu.
  6. See the Documentation for info about how to use the GUI app. The GUI corresponds to the command-line options.

Install the pyftfeatfreeze CLI app

This tool requires Python 3.6 or above to be installed first. Get it from or your package manager.

We recommend using pipx to install Python command line tools. Pipx tucks them away neatly on your computer and gives you an easy way to add, update and remove Python tools on all platforms, without leaving a mess in your Python installation.

pipx install opentype-feature-freezer

Other methods

Install it with pip, as any other Python package.

# This is best done inside a virtual environment, so you don't pollute
# your Python installation and need no special privileges to install anything.

pip install --upgrade opentype-feature-freezer

If this does not work, try:

python3 -m pip install --user --upgrade opentype-feature-freezer

Development version

pip install --upgrade git+

If this does not work, use:

python3 -m pip install --user --upgrade git+



Let’s say you have the font CharisSIL-R.ttf (with the menu name “Charis SIL”), and this font includes true smallcaps accessible via the OpenType Layout features c2sc (for uppercase) and smcp (for lowercase). Let’s say that you’d like to make a second font where the true smallcaps are available by default. Just run:

pyftfeatfreeze -f 'c2sc,smcp' -S -U SC -R 'Charis SIL/Charix,CharisSIL/Charix' CharisSIL-R.ttf CharixSC-R.ttf

You’ll get a new font CharisSIL-R.ttf (with the menu name “Charix SC”). This font will have smallcaps instead of the lowercase and uppercase letters, available in all apps.

Since the “Charis SIL” font is licensed under the OFL, and uses the Reserved Font Names “Charis” and “SIL”, I’ve specified the -R option to replace the name strings Charis SIL and CharisSIL with Charix. This way, the modified font is compliant with the OFL and I can distribute it.

The following example remaps the font so that the Bulgarian localized forms are available by default in all apps (the suffix “BG” will be added to the menu name):

pyftfeatfreeze -f 'locl' -s 'cyrl' -l 'BGR ' -S -U BG SomeFont.ttf SomeFontBG.ttf

Note: To remap features from multiple scripts or languagesystems, run the tool multiple times (taking the previous run’s output as input). Use the -S option only on the final run.

The following replaces the string Lato by Otal in all internal font names (in the name and CFF tables), without doing any “feature freezing”. This can be used to quickly change some internal font names:

pyftfeatfreeze -R 'Lato/Otal' Lato-Regular.ttf Otal-Regular.ttf

Command-line syntax

usage: pyftfeatfreeze [-h] [-f FEATURES] [-s SCRIPT] [-l LANG] [-z] [-S]
                      [-U USESUFFIX] [-R REPLACENAMES] [-i] [-r] [-n] [-v]
                      inpath [outpath]

With pyftfeatfreeze you can "freeze" some OpenType features into a font. These
features are then "on by default", even in apps that don't support OpenType
features. Internally, the tool remaps the "cmap" table of the font by applying
the specified GSUB features. Only single and alternate substitutions are

positional arguments:
  inpath                input .otf or .ttf font file
  outpath               output .otf or .ttf font file (optional)

optional arguments:
  -h, --help            show this help message and exit

options to control feature freezing:
  -f FEATURES, --features FEATURES
                        comma-separated list of OpenType feature tags, e.g.
  -s SCRIPT, --script SCRIPT
                        OpenType script tag, e.g. 'cyrl' (default: 'latn')
  -l LANG, --lang LANG  OpenType language tag, e.g. 'SRB ' (optional)
  -z, --zapnames        zap glyphnames from the font ('post' table version 3,
                        .ttf only)

options to control font renaming:
  -S, --suffix          add a suffix to the font family name (by default, the
                        suffix will be constructed from the OpenType feature
                        use a custom suffix when --suffix is provided
                        search for strings in the font naming tables and
                        replace them, format is
  -i, --info            update font version string

reporting options:
  -r, --report          report languages, scripts and features in font
  -n, --names           output names of remapped glyphs during processing
  -v, --verbose         print additional information during processing
  -V, --version         show program's version number and exit

Examples: pyftfeatfreeze -f 'c2sc,smcp' -S -U SC OpenSans.ttf OpenSansSC.ttf
pyftfeatfreeze -R 'Lato/Otal' Lato-Regular.ttf Otal-Regular.ttf

Tip: the -n option outputs a space-separated list of “frozen” glyphs. If you redirect it to a file, you can use this list as input for pyftsubset to create a small font that only includes the “frozen” glyphs.


Problem reporting

To report a problem, open an issue. You need a Github account.

Software license and disclaimer

This tool is licensed “as is” under the Apache License, Version 2.0. By using the tool, you accept all conditions of the license, including Disclaimer of Warranty and Limitation of Liability. If you use this tool, please consult if your font’s EULA allows modifications. If the font is licensed under the OFL and uses the Reserved Font Name, please use the -R option to change the Reserved Font Name to something else.


This tool is written for Python 3.6+, and uses fontTools/TTX.




To build the Python package, install Poetry:

pip install poetry


python3 -m install --user --upgrade poetry

then in the main folder of the project run:

poetry build


To build the DMG & EXE, you need macOS. In the app subfolder, run ./macdeploy all