Agent Skills: Mobile Design System

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.

When to Use

This skill is applicable to execute the workflow or actions described in the overview.