expo-design-system

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---
name: expo-design-system
description: Framework (OSS). Build and maintain a design system inside an Expo app - a reusable theme of design tokens (color, spacing, typography, radius, shadow, motion), reusable component structure with variant/size/state prop conventions, and rules for when to extract a repeated view into a shared component. Use when creating or organizing theme files and design tokens (theme.ts / theme/), extending an existing theme or styling library (NativeWind, Tamagui, Restyle, Unistyles) in its own idiom, standardizing styles so screens (including AI-generated ones) look consistent and polished, fixing an app that looks AI-generated or generic instead of native (the named native-slop tells), building an in-app component library, or auditing an app for design-system drift (hardcoded colors, spacing, fonts). For platform styling specifics (semantic colors, HIG rules, native controls) use expo-native-ui; for folder layout of a new app use expo-project-structure.
version: 1.0.0
license: MIT
---

# Expo Design Systems

Make every screen in an app draw from one visual source of truth: a token theme and a small set of reusable components. This skill defines where tokens live, what they cover, how reusable components are shaped, and when a repeated view earns promotion into the system.

Sibling skills own the layers around this one:

- `expo-native-ui` - platform styling rules (HIG, semantic colors, controls, shadows syntax). Follow it for **what values look native**; follow this skill for **where values live and how they're reused**.
- `expo-project-structure` - folder skeleton for new apps.

For Tailwind projects, keep tokens in `global.css` as CSS variables and follow the styling library's own setup guidance. The scales and naming in this skill still apply; only the storage format changes.

## References

Consult these resources as needed:

```
references/
  audit.md        Audit an existing app for design-system drift: grep checks,
                  scoring rubric, incremental adoption plan, and templates for
                  documenting or extending components
  native-slop.md  The 20 named anti-pattern tells of AI-generated apps (The Web
                  Modal, Everything's a Card, ...) with grep checks for the greppable ones
```

## Adopt Before You Build

In an app that already has screens, the first move is detection, not construction. Before writing any token file:

1. **Look for a declared system.** Check `package.json` for a styling library - NativeWind/Tailwind, Tamagui, Restyle, Unistyles, styled-components. Then look for a token file: `theme.ts`, `src/theme/`, `constants/theme.ts`, or `constants/Colors.ts` (the create-expo-app default).
2. **If one exists, it is the source of truth.** Extend it in its own idiom - its names, its scale, its storage format. Audit drift against that system, not against the examples below.
3. **If only de facto values exist** - the same greys and paddings repeated across screens, no theme file - there is no system yet. Those values are the input to the scales, not the authority: derive tokens from the most frequent ones, snapped to the 4-point grid (`references/audit.md` §5).
4. **Never introduce a second system beside an existing one.** A fresh `src/theme/` next to a Tamagui config is design-system drift, not adoption.

Only when nothing exists do the defaults below apply as written.

## The Theme

In an app without an existing system, all design tokens live under `src/theme/`. In a project without a `src/` folder (the default `create-expo-app` template has `app/`, `components/`, and `constants/` at the root), use the equivalent top-level location - typically `theme/` or the existing `constants/` - and keep the same file layout. Start small and split by token class as it grows:

```
src/theme/
  colors.ts       # see expo-native-ui "Colors" for the palette pattern
  spacing.ts
  typography.ts
  radius.ts
  shadows.ts
  motion.ts
  index.ts        # re-exports every