<!-- SPDX-License-Identifier: MIT -->
<!-- SPDX-FileCopyrightText: 2025-2026 Marcus Quinn -->

# Design System: Claude — Typography Rules

## Font Family

- **Headline**: `Anthropic Serif`, with fallback: `Georgia`
- **Body / UI**: `Anthropic Sans`, with fallback: `Arial`
- **Code**: `Anthropic Mono`, with fallback: `Arial`

*Note: These are custom typefaces. For external implementations, Georgia serves as the serif substitute and system-ui/Inter as the sans substitute.*

## Hierarchy

| Role | Font | Size | Weight | Line Height | Letter Spacing | Notes |
|------|------|------|--------|-------------|----------------|-------|
| Display / Hero | Anthropic Serif | 64px (4rem) | 500 | 1.10 (tight) | normal | Maximum impact, book-title presence |
| Section Heading | Anthropic Serif | 52px (3.25rem) | 500 | 1.20 (tight) | normal | Feature section anchors |
| Sub-heading Large | Anthropic Serif | 36–36.8px (~2.3rem) | 500 | 1.30 | normal | Secondary section markers |
| Sub-heading | Anthropic Serif | 32px (2rem) | 500 | 1.10 (tight) | normal | Card titles, feature names |
| Sub-heading Small | Anthropic Serif | 25–25.6px (~1.6rem) | 500 | 1.20 | normal | Smaller section titles |
| Feature Title | Anthropic Serif | 20.8px (1.3rem) | 500 | 1.20 | normal | Small feature headings |
| Body Serif | Anthropic Serif | 17px (1.06rem) | 400 | 1.60 (relaxed) | normal | Serif body text (editorial passages) |
| Body Large | Anthropic Sans | 20px (1.25rem) | 400 | 1.60 (relaxed) | normal | Intro paragraphs |
| Body / Nav | Anthropic Sans | 17px (1.06rem) | 400–500 | 1.00–1.60 | normal | Navigation links, UI text |
| Body Standard | Anthropic Sans | 16px (1rem) | 400–500 | 1.25–1.60 | normal | Standard body, button text |
| Body Small | Anthropic Sans | 15px (0.94rem) | 400–500 | 1.00–1.60 | normal | Compact body text |
| Caption | Anthropic Sans | 14px (0.88rem) | 400 | 1.43 | normal | Metadata, descriptions |
| Label | Anthropic Sans | 12px (0.75rem) | 400–500 | 1.25–1.60 | 0.12px | Badges, small labels |
| Overline | Anthropic Sans | 10px (0.63rem) | 400 | 1.60 | 0.5px | Uppercase overline labels |
| Micro | Anthropic Sans | 9.6px (0.6rem) | 400 | 1.60 | 0.096px | Smallest text |
| Code | Anthropic Mono | 15px (0.94rem) | 400 | 1.60 | -0.32px | Inline code, terminal |

## Principles

- **Serif for authority, sans for utility**: Anthropic Serif carries all headline content with medium weight (500), giving every heading the gravitas of a published title. Anthropic Sans handles all functional UI text — buttons, labels, navigation — with quiet efficiency.
- **Single weight for serifs**: All Anthropic Serif headings use weight 500 — no bold, no light. This creates a consistent "voice" across all headline sizes, as if the same author wrote every heading.
- **Relaxed body line-height**: Most body text uses 1.60 line-height — significantly more generous than typical tech sites (1.4–1.5). This creates a reading experience closer to a book than a dashboard.
- **Tight-but-not-compressed headings**: Line-heights of 1.10–1.30 for headings are tight but never claustrophobic. The serif letterforms need breathing room that sans-serif fonts don't.
- **Micro letter-spacing on labels**: Small sans text (12px and below) uses deliberate letter-spacing (0.12px–0.5px) to maintain readability at tiny sizes.
