Expo Design System

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

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

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