Fonts in coding agents

What an agent prints

An agent's interface is text in a grid of cells. Around the code and the prose it draws panels and tables with box-drawing characters, progress with block elements, spinners with Braille patterns, and steps and results with arrows, check marks and bullets.

╭─ plan ─────────────────────╮
│ ⠋ reading 12 files         │
│ ✓ tests pass  ▕████▌       │
│ → edit src/fonts.ts        │
╰────────────────────────────╯Copy

When the font lacks one of these characters, the terminal draws it from another font. That font usually has another width, so the columns after the character stop lining up.

What the font needs

• Symbols have the same cell width as every other glyph.
• The 0 and O are drawn apart, and so are 1, l and I, because agents print hashes, IDs, tokens and paths that people copy.
• Ligatures are off until you turn them on, so -> and != show the characters the agent wrote and a diff shows what changed.
• The font itself has the box-drawing, block and Braille ranges.
• The weights stay legible when an interface bolds a heading or dims a note.

Katagami Mono

Katagami Mono draws the status characters ⏺ ⎿ ✓ ✗ ✔ ✘ ● ○ ◉ ◆ ▶ ▸ › … ⏵ ⏸ ⏹ ⚠ ✕ ★ ☆ ✻ ✢ ✳ ✶ ✽ • → ← ↑ ↓.

Its cell is 1,280 units wide, which is 0.625 em. Code ligatures for ->, =>, !=, == and >= stay off until you turn on dlig, and each character in a ligature keeps its own cell.

Terminal settings

Install KatagamiMono[wght].ttf from the download page first, then restart the terminal.

Agent-native fonts covers what an agent needs to find and install a font on its own.