Modifying a variable font with no source files

For Prepbook (the recipe app I'm working on) I wanted to use the font iA Writer Quattro. It has that analog "typewriter" feel you get from monospace fonts, but much more readable and compact because it has 4 character widths ("quattro") rather than one ("mono"). You can read more about in this post.

However, for the use case of displaying recipes, the wide punctuation characters and narrow fraction glyphs hurt readability.

The iA fonts are open source with a license that permits modifications, but the source files were never published - so I wondered if I could edit the compiled variable fonts without breaking anything.

With the help of Claude Code I built a pipeline that tweaks the font:

• Tightening sidebearings on punctuation

• Tweaking specific glyph shapes

• Completely rebuilding the fraction glyphs

• Adjusting the base font weight slightly

To my surprise, it went smoothly and the font retained its variable axis! I made it configurable so I can keep iterating without rewriting the pipeline. Repo is available here if anyone's interested: prepbook-quattro