---
id: cffsubr
version: "0.4.0"
license: Apache 2.0
license_treatment: permissive
maintenance: active
---

# cffsubr — Standalone CFF subroutinizer based on the AFDKO tx tool

License: permissive · Maintenance: active · Downloads: 94.7K/mo

## What it is and what it does

cffsubr is a standalone tool for optimizing CFF (Compact Font Format) font files by identifying repeated glyph outline patterns and consolidating them into subroutines. This reduces font file size without changing the visual appearance of glyphs. It is based on the AFDKO tx tool from Adobe and wraps that functionality for Python users.

The package depends only on fontTools and runs on Python 3.10 and later across Windows, macOS, and Linux. It is actively maintained and marked as production-stable. The project is small but focused, with no known security vulnerabilities.

Use it for:

- Optimize web fonts before deployment to reduce bandwidth and improve page load times
- Compress font files in font libraries or design tools that work with CFF outlines
- Batch-process font collections to standardize file sizes across a design system
- Prepare fonts for embedded systems or devices with storage constraints

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Subroutinizes CFF (Compact Font Format) font files by identifying and extracting repeated glyph outlines into reusable subroutines, reducing file size.

Yes, if you work with CFF fonts and need to reduce file size. The package is actively maintained, has no security issues, uses a permissive license, and solves a specific problem well. Install friction is moderate but manageable; the single dependency is standard in font tooling. Not necessary if you don't work with CFF fonts or already use other font optimization tools.

## Install

pip install cffsubr
uv add cffsubr
poetry add cffsubr

## Installing cffsubr

Before you install: Medium install friction due to compiled wheels for multiple platforms; actively maintained with recent commits and production-stable status. Single runtime dependency on fontTools.

License in practice: Apache 2.0 permissive license allows use in commercial and open-source projects with minimal restrictions; attribution required.

Quickstart:

pip install cffsubr

from cffsubr import subroutinize
subroutinize('input.otf', 'output.otf')

Requires Python 3.10 or later; fontTools must be installed as a runtime dependency.

Verify before relying:

- Whether the package provides a command-line interface in addition to Python API
- Performance characteristics and typical compression ratios achieved
- Whether it handles variable fonts or only static CFF outlines

## Package facts

- License: Apache 2.0 (permissive)
- Python support: supports_current
- Install friction: medium
- Maintenance: active
- Downloads: 94.7K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

CFF font subroutinizer, font file compression, glyph outline deduplication, compact font format optimization, font subsetting and optimization, AFDKO subroutinizer, reduce font file size, font-optimization, cff-format

[View on SkillFed](https://skillfed.io/packages/cffsubr) · [View on PyPI](https://pypi.org/project/cffsubr/)