Performance Expert Skill
Expert in performance optimization for React, Next.js, NestJS applications, MongoDB, and AWS infrastructure.
When to Use This Skill Optimizing React components or Next.js pages Improving API response times Optimizing database queries Analyzing bundle sizes Implementing caching strategies Optimizing images or assets Configuring CDN or caching Reviewing Core Web Vitals Project Context Discovery Check .agent/SYSTEM/ARCHITECTURE.md for performance architecture Identify performance tools (Lighthouse CI, APM) Review existing optimizations and caching strategies Check for [project]-performance-expert skill Core Performance Principles Frontend (React/Next.js)
Bundle Optimization: Code splitting, dynamic imports, tree shaking, remove unused deps
React Optimization: useMemo, useCallback, React.memo, virtualization, lazy loading
Next.js: Server Components, SSG, ISR, next/image, font optimization
Assets: WebP images, font subset, CSS minify, Gzip/Brotli
Backend (NestJS)
API Response Times: Target < 200ms (p95), caching, background jobs, connection pooling
Query Optimization: Indexes, projections, pagination, optimized aggregations
Database (MongoDB)
Indexes: On frequently queried fields, compound indexes, monitor usage
Queries: Early $match, projection before expensive ops, sort with indexes
Infrastructure (AWS)
CDN: CloudFront caching, cache headers, edge optimization
Lambda: Cold start optimization, memory allocation, provisioned concurrency
Performance Metrics Frontend (Core Web Vitals) LCP: < 2.5s FID: < 100ms CLS: < 0.1 FCP: < 1.8s Backend API p50: < 100ms API p95: < 200ms DB Query p95: < 50ms Error Rate: < 0.1% Quick Checklist Frontend Bundle size < 200KB initial Code splitting implemented Images optimized and lazy loaded React components memoized Backend Database queries optimized Indexes created and used Caching implemented Background jobs for heavy operations
For complete React memoization patterns, Next.js optimization examples, database query optimization code, caching strategy implementation, N+1 query solutions, performance testing commands, and detailed checklists, see: references/full-guide.md