What it does
fontc is an open-source Rust compiler for font sources. It accepts Glyphs, Designspace and Fontra inputs, with debugging and comparison tools for type engineers evaluating font builds.
From a repository checkout with Rust installed, the documented example cargo run -p fontc -- resources/testdata/wght_var.designspace compiles a supplied Designspace source. Parallel examples cover Glyphs and Fontra files. Add the emit-debug option to write intermediate troubleshooting files into the build directory’s debug folder.
For a family already built through fontmake, compare the outputs before changing its release pipeline. The fontc_crater tool compiles many families for comparison, and ttx_diff examines differences in their XML font representations. The project tracks matching results and differences that have been investigated.
fontc has its own Rust compilation path, from source through an intermediate representation to a font binary. Compatibility is still being expanded across source families; success with one test font does not establish identical output for every existing build.
Strengths
- The repository supplies build examples for three font-source formats.
- Debug output and compiler-comparison tools support investigation.
Watch out for
- Compatibility with an existing build needs family-specific comparison.
Best for
- Type engineers evaluating Rust-based font compilation
Sources
- fontc README (Oct 27, 2026)
- fontc Apache License (Oct 27, 2026)