How Alacritty's Font Scaling Works

How Alacritty's Font Scaling Works | Generated by AI

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Now I have the full picture. Here’s the answer:

Why your font size resets every time you open Alacritty:

When you scale the font size with Cmd+= / Cmd+- at runtime, it only changes display.font_size in memory. The code in event.rs:921-927 shows this clearly:

fn change_font_size(&mut self, delta: f32) {
    let new_size = self.display.font_size.as_px().round() + delta;
    self.display.font_size = FontSize::from_px(new_size);
    // ... applies to display only, never written to config
}

On the next launch, Alacritty reads the config file and applies config.font.size() again. Since you have NO config file (~/.config/alacritty/alacritty.toml doesn’t exist), it uses the hardcoded default: 11.25 pt (see font.rs:137).

The ResetFontSize action (Ctrl+Cmd+0 on macOS) confirms this — it resets back to the config value:

fn reset_font_size(&mut self) {
    self.display.font_size = self.config.font.size().scale(scale_factor);
}

The fix: create a config file with your desired size:

mkdir -p ~/.config/alacritty
cat > ~/.config/alacritty/alacritty.toml << 'EOF'
[font]
size = 16.0

[font.normal]
family = "Menlo"
EOF

Adjust size to whatever you want (16.0 is a good starting point for Retina Macs). The font size is in points, and Alacritty applies DPI scaling automatically via scale_factor.

Key insight from the code (window_context.rs:277-280): even on config reload, Alacritty preserves your runtime font size change IF it differs from the old config. But on a fresh launch, there’s nothing to preserve — it always reads from config, or falls back to the 11.25 pt default.

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