expo-design-system

Design

Airbnb-DLS-aligned design system engineering for Expo / React Native apps targeting both web and native iOS, built on Unistyles v3, Reanimated, Skia, and FlashList. Use whenever building, reviewing, or refactoring shared UI — design tokens, theming, variant-driven component APIs, typography, spacing, cross-platform web/iOS parity, native-feel performance, or complex surfaces like calendars and drawing canvases (examples use a clinic app). Covers token architecture, theming, component API contracts (variants over style props), web/iOS parity (Unistyles `_web` hover/focus/cursor, Platform splits, one shared theme), the Unistyles styling engine, and governance. Trigger even when the user does not say "design system" but is creating or changing reusable React Native components, tokens, theme code, or making a component behave natively on both web and iOS. Teaches how to BUILD the design system; pair with expo-react-native-coder for features and expo-ios-hig for iOS native-feel decisions.

QUICK START

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Airbnb DLS Expo React Native Design System Best Practices

Opinionated, strict design system engineering for Expo / React Native apps on the New Architecture, targeting both web and native iOS. Contains 63 rules across 11 categories, prioritized by impact. Derived from Airbnb's Design Language System (DLS), the Unistyles v3 documentation, and the React Native ecosystem (Reanimated, Gesture Handler, Skia, FlashList, Expo SDK). The styling engine is Unistyles v3; the component API follows the Airbnb DLS pattern of variant props over style escape hatches.

Mandated Architecture Alignment

This skill is the infrastructure layer — it teaches how to BUILD the design system itself, the React Native counterpart to ios-design-system. All code examples follow the same non-negotiable constraints:

Feature modules import @clinic/design-system + domain; never another feature's internals
The design system owns the Unistyles theme (tokens, breakpoints) and exports a curated public surface
Reuse before you build: read the index, extend a variant, promote on the second use — never a parallel local component
Components expose variant and slot props (Airbnb DLS); no raw style escape hatch
Animation and gestures run on the UI thread (Reanimated worklets + Gesture Handler)
Lists use FlashList; the body-chart drawing surface uses React Native Skia
One source feels native on both web and iOS: Unistyles _web pseudo-states and Platform splits, never a forked web stylesheet
Targets the New Architecture (Fabric/JSI), Expo SDK 53+ / React Native 0.81+

Scope & Relationship to Sibling Skills

Sibling Skill	Its Focus	This Skill's Focus
`ios-design-system`	The SwiftUI design system for the same clinic app	The Expo / React Native counterpart
`expo-react-native-coder`	Feature development (screens, navigation, data fetching)	Design system infrastructure (tokens, components, theming)
`expo-react-native-performance`	App-wide performance optimization	Native-feel performance inside the design system
`react`	General React patterns	Expo / React Native design system specifics
`expo-ios-hig`	iOS native-feel decisions (navigation, system controls, Liquid Glass)	Cross-platform token/component architecture + web/iOS parity

Clinic Architecture Contract (Expo / React Native)

All guidance in this skill assumes the clinic modular architecture:

Feature modules depend on @clinic/design-system + domain only; the app target wires navigation (Expo Router) and dependency injection
The design system is a local package with a single public entry; raw token layers stay private
Token source of truth is the Unistyles theme; features never define local tokens
Server state uses TanStack Query: reads default to stale-while-revalidate, writes are optimistic and queued for offline sync
The New Architecture is required for Unistyles v3, Reanimated worklets, Skia, and FlashList v2

When to Apply

Reference these guidelines when:

Setting up a design system for a new Expo / React Native app
Building token architecture (colors, typography, spacing, radius, elevation) in the Unistyles theme
Designing component APIs — variants, slots, controlled/uncontrolled state, refs, accessibility
Authoring component styles with Unistyles StyleSheet, variants, and dynamic functions
Building the calendar, treatment-note editor, or Skia body-chart drawing surfaces
Migrating ad-hoc styles to a governed token system
Reviewing PRs for raw colors, inline styles, leaked style props, or feature-local tokens
Tuning native feel — list virtualization, UI-thread animation, gestures, haptics, safe areas
Making a component render and feel native on both web and iOS — hover/focus/cursor, Platform splits, and safe-area/haptics divergences
Deciding whether to build new or reuse — checking the design system index, extending vs forking, or using a native/@expo/ui control instead of reimplementing one

Rule Categories by Priority

Priority	Category	Impact	Prefix	Rules
1	Token Architecture	CRITICAL	`token-`	6
2	Theming & Adaptivity	CRITICAL	`theme-`	5
3	Component API Contracts	CRITICAL	`api-`	8
4	Cross-Platform Parity	CRITICAL	`platform-`	5
5	Reuse & System Fit	HIGH	`reuse-`	4
6	Styling Engine (Unistyles)	HIGH	`style-`	6
7	Typography & Iconography	HIGH	`type-`	5
8	Spacing, Layout & Safe Areas	HIGH	`space-`	5
9	Native-Feel & Performance	HIGH	`perf-`	7
10	Complex Domain Components	MEDIUM-HIGH	`domain-`	6
11	Governance & Consistency	MEDIUM	`govern-`	6

Quick Reference

1. Token Architecture (CRITICAL)

token-three-layer-scale - Layer tokens as raw, semantic, and component scales
token-define-in-unistyles-theme - Keep the Unistyles theme as the single token source
token-no-raw-values-in-components - Route every color and size through tokens
token-semantic-naming - Name tokens by role, not by value
token-elevation-pairs - Tokenize elevation as surface and shadow pairs
token-avoid-over-abstraction - Stop at three token layers

2. Theming & Adaptivity (CRITICAL)

theme-runtime-not-rerender - Switch themes via the runtime, no re-render
theme-stylesheet-theme-arg - Read theme from the StyleSheet argument
theme-adaptive-system - Follow the system color scheme by default
theme-breakpoints-responsive - Use breakpoints, not Dimensions checks
theme-config-single-module - One typed config module for themes and breakpoints

3. Component API Contracts (CRITICAL)

api-variants-over-style-prop - Express visual options as variant props
api-no-style-escape-hatch - No raw style prop on components
api-compound-variants - Compound variants over per-combination components
api-slots-for-composition - Slot props over a prop per element
api-controlled-uncontrolled - Support controlled and uncontrolled state
api-forward-ref - Forward refs from leaf components
api-accessibility-in-contract - Require accessibility props in the contract
api-aschild-polymorphism - Offer asChild instead of wrapper nesting

4. Cross-Platform Parity (CRITICAL)

platform-web-pseudo-states - Add web hover, focus, and cursor to interactive components
platform-guard-native-only - Guard native-only APIs behind Platform checks with web fallbacks
platform-divergence-split - Isolate platform differences behind one component API
platform-input-model - Design for pointer and touch, never hover-only
platform-shared-theme-parity - One theme for web and native, with a known divergence map

5. Reuse & System Fit (HIGH)

reuse-inventory-first - Read the design system index before writing any style
reuse-extend-not-fork - Extend a shared component with a variant, don't fork a local one
reuse-promote-on-second-use - Promote a pattern to the system on its second use
reuse-platform-component-first - Reach for a native control before reimplementing one

6. Styling Engine (Unistyles) (HIGH)

style-stylesheet-create - StyleSheet.create over inline objects
style-variants-api - Variants over ternary style arrays
style-dynamic-functions - Dynamic functions for prop-driven values
style-no-inline-array-merge - No inline array merges in lists
style-withunistyles-third-party - Theme third-party components with withUnistyles
style-press-states-from-variants - Press and disabled states as variants

7. Typography & Iconography (HIGH)

type-scale-tokens - Define a named typography scale
type-respect-font-scaling - Respect OS font scaling
type-text-component-wrapper - Route text through one typed component
type-font-loading-expo-font - Load fonts before first paint
type-icon-registry - Centralize icons in a typed registry

8. Spacing, Layout & Safe Areas (HIGH)

space-spacing-scale - Use a spacing scale on a 4pt grid
space-safe-area-insets - Apply safe-area insets at screen edges
space-touch-targets - Size touch targets to at least 44 points
space-gap-over-margins - Use gap over per-child margins
space-radius-tokens - Tokenize corner radius by role

9. Native-Feel & Performance (HIGH)

perf-flashlist-for-lists - FlashList over ScrollView lists
perf-reanimated-ui-thread - Animate on the UI thread
perf-gesture-handler - Gesture Handler over PanResponder
perf-expo-image - Load images with expo-image and caching
perf-memoize-list-items - Memoize rows and callbacks
perf-haptics-key-actions - Add haptics on confirmations and toggles
perf-defer-offscreen-work - Defer work past transitions

10. Complex Domain Components (MEDIUM-HIGH)

domain-calendar-virtualization - Virtualize the appointment calendar by day
domain-note-editor-autosave - Offline-first debounced note autosave
domain-bodychart-skia-canvas - Draw body charts on a Skia canvas
domain-bodychart-gesture-paths - Capture strokes via gestures and shared values
domain-compose-from-primitives - Build domain components from primitives
domain-optimistic-writes - Render optimistic UI for writes

11. Governance & Consistency (MEDIUM)

govern-design-system-package - Package the design system with one entry
govern-lint-no-raw-values - Lint against raw colors and inline styles
govern-prevent-local-tokens - Prevent feature-local tokens
govern-storybook-catalog - Catalog component variants in Storybook
govern-naming-conventions - Enforce one naming convention
govern-incremental-migration - Migrate to tokens incrementally

How to Use

Read individual reference files for detailed explanations and code examples:

Section definitions - Category structure and impact levels
Rule template - Template for adding new rules

Reference Files

File	Description
references/_sections.md	Category definitions and ordering
assets/templates/_template.md	Template for new rules
metadata.json	Version and reference information