Typography
The platform's system font MUST be used. Establish a type scale with clear roles — don't invent sizes ad-hoc.
Platform system fonts:
- Apple: SF Pro (iOS/macOS), New York (serif alternative)
- Android: Roboto, or system default via Material type system
- Windows: Segoe UI Variable
- Web: System font stack (
system-ui, -apple-system, sans-serif)
Defaults when no design system exists:
- Body text: 14-17pt (16px is the safest cross-platform default)
- Minimum readable size: 11-12pt for captions/labels, text MUST NOT be smaller
- Line height: 1.4x-1.5x font size for body text
- Heading scale: Use the platform's built-in type scale (Dynamic Type, Material type tokens, Fluent type ramp) rather than inventing sizes
General principles:
- Limit to 2-3 font weights per screen (regular, medium/semibold, bold)
- All-caps SHOULD be avoided for more than a few words — harms readability and screen reader experience
- Paragraph width: 45-75 characters for comfortable reading
- See agenticdevelopercookbook://guidelines/implementing/accessibility/accessibility for Dynamic Type / font scaling requirements
References: