--- name: vercel-react-best-practices description: React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.js code to ensure optimal performance patterns. Triggers on tasks involving React components, Next.js pages, data fetching, bundle optimization, or performance improvements. license: MIT metadata: author: vercel version: "1.0.0" --- # Vercel React Best Practices Comprehensive performance optimization guide for React and Next.js applications, maintained by Vercel. Contains 70 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation. ## When to Apply Reference these guidelines when: - Writing new React components or Next.js pages - Implementing data fetching (client or server-side) - Reviewing code for performance issues - Refactoring existing React/Next.js code - Optimizing bundle size or load times ## Rule Categories by Priority | Priority | Category | Impact | Prefix | |----------|----------|--------|--------| | 1 | Eliminating Waterfalls | CRITICAL | `async-` | | 2 | Bundle Size Optimization | CRITICAL | `bundle-` | | 3 | Server-Side Performance | HIGH | `server-` | | 4 | Client-Side Data Fetching | MEDIUM-HIGH | `client-` | | 5 | Re-render Optimization | MEDIUM | `rerender-` | | 6 | Rendering Performance | MEDIUM | `rendering-` | | 7 | JavaScript Performance | LOW-MEDIUM | `js-` | | 8 | Advanced Patterns | LOW | `advanced-` | ## Quick Reference ### 1. Eliminating Waterfalls (CRITICAL) - `async-cheap-condition-before-await` - Check cheap sync conditions before awaiting flags or remote values - `async-defer-await` - Move await into branches where actually used - `async-parallel` - Use Promise.all() for independent operations - `async-dependencies` - Use better-all for partial dependencies - `async-api-routes` - Start promises early, await late in API routes - `async-suspense-boundaries` - Use Suspense to stream content ### 2. Bundle Size Optimization (CRITICAL) - `bundle-barrel-imports` - Import directly, avoid barrel files - `bundle-analyzable-paths` - Prefer statically analyzable import and file-system paths to avoid broad bundles and traces - `bundle-dynamic-imports` - Use next/dynamic for heavy components - `bundle-defer-third-party` - Load analytics/logging after hydration - `bundle-conditional` - Load modules only when feature is activated - `bundle-preload` - Preload on hover/focus for perceived speed ### 3. Server-Side Performance (HIGH) - `server-auth-actions` - Authenticate server actions like API routes - `server-cache-react` - Use React.cache() for per-request deduplication - `server-cache-lru` - Use LRU cache for cross-request caching - `server-dedup-props` - Avoid duplicate serialization in RSC props - `server-hoist-static-io` - Hoist static I/O (fonts, logos) to module level - `server-no