React Performance: Client — SWR Deduplication. Keywords: swr dedup cache revalidate. Platform: React/Next.js. Description: Use SWR for automatic request deduplication and caching. Do: Use useSWR for client data fetching. Don't: Manual fetch in useEffect. Good Example: const { data } = useSWR('/api/users', fetcher). Bad Example: useEffect(() => { fetch('/api/users').then(setUsers) }, []). Severity: Medium-High.