Caesium is a cursive typeface for programming, derived as a hard fork from Cascadia Code. While it inherits some of Cascadia’s structure, Caesium takes a more radical approach in design.

Downloads

The built font files are committed under exported/ in this repo.

• Static TTFs: exported/static/Caesium-*.ttf
• Variable fonts: exported/variable/CaesiumVF-*.ttf

You can download the latest archive from the release page.

Fonts are distributed in both static and variable formats. For Windows users, static font files are recommended for kerning.

Feature Lookup

Tag	Default	Description
kern	On	Enables submono spacing.
calt	On	Optimizes 0x/0b in literals; centers colons between digits.
ss01	Off	Enables more cursive letterforms.
ss02	Off	Suppresses cursive letterforms.
ss18	Off	Enables dotted zeros (defaults to slashed).
dlig	Off	Links consecutive horizontal bars (e.g. ###, ===).
pwid	Off	Enables proportional spacing (breaks column grids).

Note that ss01 and ss02 are mutually exclusive; do not enable both of them.

Design

Glyph categories vary:

• Lowercase letters: cursive with a 2° slant.
• Uppercase letters: roman with a 1° slant.
• Symbols and digits: upright.

This gives Caesium rhythm, lends characters a script-like feel, and improves legibility.

Cursiveness

By default, Caesium doesn’t fully adopt cursive forms. For example, ⟨a⟩ and ⟨g⟩ are two-storey (or maybe 1.5-storey?), which gives letters unique shapes and improves the differentiation between similar characters.

With the OpenType feature ss01 enabled, or by default in italic subfamilies (though they can hardly be called orthodox italics), more letters become cursive. The OpenType feature ss02 can be used to revert cursive italics, and makes ⟨z⟩ more distinguishable from ⟨3⟩.

Submono

Another attractive feature is “submono”: letters inside a word adjust their width and position, while the total width of the word remains unchanged. This allows letters that should have been wide, like ⟨W⟩ and ⟨m⟩, to be relaxed and those that should be narrow, like ⟨I⟩ and ⟨t⟩, to be tightened, resulting in more proportional glyphs.

This feature, nominally embodied as kern, is not implemented by altering the advance width of each glyph, but by replacing the glyph face (the filled area) to create a visual shift. Therefore, it won’t break column grids where strict monospaced glyphs are required.

Weight Mapping

Caesium’s default weight (Regular) is lighter than Cascadia’s; it aligns better with other fonts. To replicate Cascadia’s original Regular weight, use Caesium Medium.

Coding Ligatures

The author is not a fan of coding ligatures, so Caesium doesn’t include (most of) them. However, there are two exceptions:

• For consistency with digits, ⟨x⟩ and ⟨b⟩ turn into roman forms when part of integer literals. This is implemented by the calt feature, which should be on by default.
• To link adjacent bars, e.g. to make consecutive equal signs a double line, you may enable the dlig feature, which should be off by default.

Misc Optimization

• Enlarged, dot‑like punctuation.
• Curved commas and quotation marks.
• Slashed zeros (including super/subscripts).

Caesium uses slashed zeros by default, while Cascadia uses dotted ones. To use the latter form, you may enable the feature ss18.

Additionally, analogous to the concept of duospaced fonts, Caesium has the feature pwid. Enabling this feature can make the text more proportional and suitable for regular text.

Character Coverage

• Adobe Latin 3.
• Adobe Greek 1.
• Cyrillic with regional variants.
• Powerline symbols.
• Fish prompt symbols.
• Box drawings.
• Block elements.
• Control symbols.
• Arrows and keyboard symbols.

As you can see, lowercase Greek, Cyrillic, arrows and other symbols are fully redesigned.

Demo in Use

(This theme is called Aqua.)

Fallback and Pairing

It’s recommended to use the original Cascadia as a fallback for Latin/Cyrillic/Arabic characters, and 方正巴龙草书黑体 (commercial) or 明鉴草书黑体 (SIL, in progress) for Han. These Han fonts are niche and motivated me to make this project public.

Tools for Development

• scripts/plist.js: Parses a .glyphs file (ASCII property list) into a JavaScript object.
• scripts/apply.js: Applies submono feature lookups into a .glyphs file and writes a modified file.
• scripts/finalize.js: Post-processes exported .ttf metadata tables. Requires ttx from fonttools.

Building from sources requires Glyphs.app on macOS. Typical flow: run apply.js on the .glyphs source, export from Glyphs, then run finalize.js.

License

Caesium is distributed under the SIL Open Font License 1.1. “Caesium” is a font name reserved by me; “Cascadia” is reserved by Microsoft. See the LICENSE file for details.