Typography

Type is most of your UI. The system does the hard parts — optical sizes, tracking tables, Dynamic Type — if you use its APIs. This skill covers when to trust the system, how to build hierarchy deliberately, and what custom fonts owe you back.

When This Skill Activates

• Choosing fonts or building a type hierarchy for a screen or app
• Text truncating, cramping, or breaking under larger Dynamic Type sizes
• Adopting a custom/brand font (and keeping accessibility)
• Display typesetting: hero numbers, stats, editorial headlines

Rule 1: text styles first

Predefined styles (Large Title → Caption 2) are weight + size + leading combos with Dynamic Type support built in — and different styles scale differently (body grows more than footnote), which manual font sizes can't replicate.

• Build hierarchy from 2–3 text styles + emphasized variants (bold trait — the actual weight varies per style: some go medium→semibold, others bold→heavy) before reaching for new fonts.
• Semantic colors + text styles together give dark mode, contrast, and Dynamic Type for free.
• macOS supports text styles (without Dynamic Type); design Mac type at 100% — no iOS-style scaling assumptions.

Rule 2: let optical sizes and tracking work

• San Francisco blends Text→Display designs continuously between 17 and 28pt (below: sturdier letterforms, looser tracking for legibility; above: tighter, more refined). System font APIs do this automatically — hardcoded single-cut fonts don't.
• Tracking, not kerning, for letterspacing — tracking is size-specific and lets the OS disable clashing features (ligatures). Override system tracking only in exceptional cases.
• Truncation pressure? Use allowsTightening (default-tightening-for-truncation) instead of manually squeezing — and prefer wrapping to truncating (line limit 0 on labels that matter).
• Line height moves only via leading traits: tight = −2pt, loose = +2pt (±1pt on watchOS); the system adds leading automatically for tall scripts (Arabic, Devanagari).

The Dynamic Type ladder (WWDC24 10074)

12 sizes: 7 default + 5 accessibility (AX1–AX5). .body runs 17pt at default up to 53pt at AX5 — roughly 3× taller, and layouts must expect that. Escalate in order:

1. Text styles — .font(.title) / preferredFont(forTextStyle:) + adjusts-for-content-size, line count 0 so text wraps instead of truncating.
2. @ScaledMetric for the non-text riding alongside (icon frames, spacing); SF Symbols scale via UIImage.SymbolConfiguration(textStyle:). Prioritize scaling essential content over decoration.
3. Switch layout axis at accessibility sizes — branch on dynamicTypeSize.isAccessibilitySize with AnyLayout(HStackLayout()) / AnyLayout(VStackLayout()) (UIKit: flip the stack axis on preferredContentSizeCategory.isAccessibilityCategory); give text the full line width and relax lineLimit.
4. Large Content Viewer — only for bars that legitimately can't grow: a tab bar takes under 10% of screen height, and scaled to accessibility sizes it would eat almost a quarter (WWDC24 10074). Scaling is always preferred; the viewer is the fallback, not the fix.

Test at all 12 sizes (Xcode Previews → Variants → Dynamic Type Variants), not just the biggest — mid-range accessibility sizes catch different wrap points.

The San Francisco family — pick by job

The width axis (Condensed / Regular / Compressed / Expanded):

• Default Regular; every non-Regular choice is a legibility decision — check it.
• Condensed: fit more text comfortably (long headlines wrap one line fewer).
• Compressed: display-only density, not body text.
• Expanded: display typesetting AND small secondary labels (wide + loose tracking).
• Width is a fourth hierarchy lever beside weight, size, color; all widths share identical vertical proportions, so mixing them never misaligns baselines. 2–3 styles are enough — pair one width with contrasting weights, one weight with contrasting widths, or oppose both for maximum display contrast.

Custom fonts: what you owe back

System fonts get Dynamic Type free; a brand font makes you the type engine:

• Scale with UIFontMetrics(forTextStyle:).scaledFont(for:) + adjusts-for-content-size, or SwiftUI Font.custom(_:size:relativeTo:); scale layout constants with @ScaledMetric.
• Test at the largest accessibility sizes — wrap to multiple lines rather than truncate.
• Verify script coverage for your locales; have a fallback plan for writing systems the brand font doesn't cover (the system stacks: system-ui, ui-rounded, ui-serif, ui-monospace on the web).
• Budget for the maintenance: tracking tables, optical sizing, and weight ramps are things SF does that a licensed font usually doesn't.

❌ Anti-patterns: hardcoded point sizes on user-facing text · kerning APIs for tracking jobs · custom font without relativeTo: (frozen size) · Compressed body text · truncation where wrapping was possible.

Output Format

Type review: Element | Current (font/size/style) | Issue (hierarchy/scaling/legibility) | Fix — check Dynamic Type at XXL + AX sizes before signing off; pairs with the contrast rules in generators/accessibility-generator.

References

• https://developer.apple.com/videos/play/wwdc2020/10175/ (The details of UI typography)
• https://developer.apple.com/videos/play/wwdc2022/110381/ (The expanded San Francisco family)
• https://developer.apple.com/fonts/ (SF + New York downloads)
• https://developer.apple.com/design/human-interface-guidelines/typography
• Related skills: design/sf-symbols (symbols align to text styles), foundation/attributed-string (rich text mechanics), generators/accessibility-generator