Mobile Design System

(Mobile-First · Touch-First · Platform-Respectful)

Philosophy: Touch-first. Battery-conscious. Platform-respectful. Offline-capable. Core Law: Mobile is NOT a small desktop. Operating Rule: Think constraints first, aesthetics second.

This skill exists to prevent desktop-thinking, AI-defaults, and unsafe assumptions when designing or building mobile applications.

1. Mobile Feasibility & Risk Index (MFRI)

Before designing or implementing any mobile feature or screen, assess feasibility.

MFRI Dimensions (1–5)

Dimension

Question

Platform Clarity

Is the target platform (iOS / Android / both) explicitly defined?

Interaction Complexity

How complex are gestures, flows, or navigation?

Performance Risk

Does this involve lists, animations, heavy state, or media?

Offline Dependence

Does the feature break or degrade without network?

Accessibility Risk

Does this impact motor, visual, or cognitive accessibility?

Score Formula

MFRI = (Platform Clarity + Accessibility Readiness)
       − (Interaction Complexity + Performance Risk + Offline Dependence)

Range: -10 → +10

Interpretation

MFRI

Meaning

Required Action

6–10

Safe

Proceed normally

3–5

Moderate

Add performance + UX validation

0–2

Risky

Simplify interactions or architecture

< 0

Dangerous

Redesign before implementation

2. Mandatory Thinking Before Any Work

⛔ STOP: Ask Before Assuming (Required)

If any of the following are not explicitly stated, you MUST ask before proceeding:

Aspect

Question

Why

Platform

iOS, Android, or both?

Affects navigation, gestures, typography

Framework

React Native, Flutter, or native?

Determines performance and patterns

Navigation

Tabs, stack, drawer?

Core UX architecture

Offline

Must it work offline?

Data & sync strategy

Devices

Phone only or tablet too?

Layout & density rules

Audience

Consumer, enterprise, accessibility needs?

Touch & readability

🚫 Never default to your favorite stack or pattern.

3. Mandatory Reference Reading (Enforced)

Universal (Always Read First)

File

Purpose

Status

mobile-design-thinking.md

Anti-memorization, context-forcing

🔴 REQUIRED FIRST

touch-psychology.md

Fitts’ Law, thumb zones, gestures

🔴 REQUIRED

mobile-performance.md

60fps, memory, battery

🔴 REQUIRED

mobile-backend.md

Offline sync, push, APIs

🔴 REQUIRED

mobile-testing.md

Device & E2E testing

🔴 REQUIRED

mobile-debugging.md

Native vs JS debugging

🔴 REQUIRED

Platform-Specific (Conditional)

Platform

File

iOS

platform-ios.md

Android

platform-android.md

Cross-platform

BOTH above

❌ If you haven’t read the platform file, you are not allowed to design UI.

4. AI Mobile Anti-Patterns (Hard Bans)

🚫 Performance Sins (Non-Negotiable)

❌ Never

Why

✅ Always

ScrollView for long lists

Memory explosion

FlatList / FlashList / ListView.builder

Inline renderItem

Re-renders all rows

useCallback + memo

Index as key

Reorder bugs

Stable ID

JS-thread animations

Jank

Native driver / GPU

console.log in prod

JS thread block

Strip logs

No memoization

Battery + perf drain

React.memo / const widgets

🚫 Touch & UX Sins

❌ Never

Why

✅ Always

Touch <44–48px

Miss taps

Min touch target

Gesture-only action

Excludes users

Button fallback

No loading state

Feels broken

Explicit feedback

No error recovery

Dead end

Retry + message

Ignore platform norms

Muscle memory broken

iOS ≠ Android

🚫 Security Sins

❌ Never

Why

✅ Always

Tokens in AsyncStorage

Easily stolen

SecureStore / Keychain

Hardcoded secrets

Reverse engineered

Env + secure storage

No SSL pinning

MITM risk

Cert pinning

Log sensitive data

PII leakage

Never log secrets

5. Platform Unification vs Divergence Matrix

UNIFY                          DIVERGE
──────────────────────────     ─────────────────────────
Business logic                Navigation behavior
Data models                    Gestures
API contracts                  Icons
Validation                     Typography
Error semantics                Pickers / dialogs

Platform Defaults

Element

iOS

Android

Font

SF Pro

Roboto

Min touch

44pt

48dp

Back

Edge swipe

System back

Sheets

Bottom sheet

Dialog / sheet

Icons

SF Symbols

Material Icons

6. Mobile UX Psychology (Non-Optional)

Fitts’ Law (Touch Reality)

Finger ≠ cursor
Accuracy is low
Reach matters more than precision

Rules:

Primary CTAs live in thumb zone
Destructive actions pushed away
No hover assumptions

7. Performance Doctrine

React Native (Required Pattern)

const Row = React.memo(({ item }) => (
  <View><Text>{item.title}</Text></View>
));

const renderItem = useCallback(
  ({ item }) => <Row item={item} />,
  []
);

<FlatList
  data={items}
  renderItem={renderItem}
  keyExtractor={(i) => i.id}
  getItemLayout={(_, i) => ({
    length: ITEM_HEIGHT,
    offset: ITEM_HEIGHT * i,
    index: i,
  })}
/>
`### Flutter (Required Pattern)`
class Item extends StatelessWidget {
  const Item({super.key});

  @override
  Widget build(BuildContext context) {
    return const Text('Static');
  }
}

const everywhere possible
Targeted rebuilds only

8. Mandatory Mobile Checkpoint

Before writing any code, you must complete this:

🧠 MOBILE CHECKPOINT

Platform:     ___________
Framework:    ___________
Files Read:   ___________

3 Principles I Will Apply:
1.
2.
3.

Anti-Patterns I Will Avoid:
1.
2.

❌ Cannot complete → go back and read.

9. Framework Decision Tree (Canonical)

Need OTA + web team → React Native + Expo
High-perf UI → Flutter
iOS only → SwiftUI
Android only → Compose

No debate without justification.

10. Release Readiness Checklist

Before Shipping

Touch targets ≥ 44–48px
Offline handled
Secure storage used
Lists optimized
Logs stripped
Tested on low-end devices
Accessibility labels present
MFRI ≥ 3

11. Related Skills

frontend-design – Visual systems & components
frontend-dev-guidelines – RN/TS architecture
backend-dev-guidelines – Mobile-safe APIs
error-tracking – Crash & performance telemetry

Final Law: Mobile users are distracted, interrupted, and impatient—often using one hand on a bad network with low battery. Design for that reality, or your app will fail quietly.