react-native-performance-reviewer

React Native / Expo Go Performance Reviewer

When to activate

Any code touch on:

• apps/mobile/** — components, screens, hooks, navigation
• libs/* libraries bundled by Metro (Expo/Hermes)
• Expo modules, SDK APIs, or native bridge call sites
• AsyncStorage, SecureStore, MMKV, or SQLite usage
• Push notification handlers or background fetch tasks
• State management (Zustand, Redux, Jotai, Context)
• Network layers, query clients (React Query, SWR, Apollo)
• FlatList, SectionList, FlashList, ScrollView, VirtualizedList
• Image components, video players, camera flows
• Reanimated, Animated API, or gesture handlers

Review workflow

1. Load references/PERFORMANCE_CHECKLIST.md and apply all sections relevant to the changed files.
2. Inspect the diff for the detection rules below.
3. Produce a severity-ordered finding list using the output format below.
4. Use assets/review-report-template.md for the full structured report.

Severity classification

Severity	Meaning
critical	Causes crashes, ANRs, OOM kills, or severe jank on mid-range devices under normal load
high	Visible jank, memory growth, or excessive battery drain on mid-range devices at moderate usage
medium	Degrades experience on low-end devices or under stress (50+ concurrent users)
low	Minor inefficiency, acceptable now but risky at scale
info	Observation with no current risk

Core detection rules

Rendering

• Flag components lacking React.memo, useCallback, or useMemo where props are objects, arrays, or functions created inline.
• Flag useEffect with no dependency array or an array including unstable references (new object/array each render).
• Flag Context providers whose value is a new object literal on every render — re-renders all consumers.
• Flag navigation screens that re-render on every tab switch due to missing React.memo or useFocusEffect misuse.

Memory & lifecycle

• Flag subscriptions, event listeners, timers, and Animated listeners not cleaned up in useEffect return.
• Flag state that accumulates over a session without a bound (unbounded log arrays, growing caches, stacked screens never popped).
• Flag useRef storing a value that updates every render (effectively a re-render vector).