perf-check

Use when measuring bundle size, detecting performance regressions, auditing slow queries, or investigating why something is slow.

Performance Check

Analyze and report on project performance metrics.

Arguments

  • /perf-check — full analysis
  • /perf-check --bundle — bundle size only
  • /perf-check --lighthouse <url> — Lighthouse audit
  • /perf-check --deps — dependency weight analysis
  • /perf-check --code — code-level pattern check

Workflow

Phase 1: Detect Scope

  • Frontend: bundle size, lighthouse, dependency weight
  • Backend: startup time, memory, dependency weight
  • Fullstack: both

Phase 2: Bundle Analysis

  • Build and measure output: du -sh dist/ build/ .next/
  • Check largest dependencies: npx -y cost-of-modules
  • Identify tree-shaking opportunities

Phase 3: Lighthouse (if URL available)

npx -y lighthouse <url> --output json --chrome-flags="--headless --no-sandbox"

Phase 4: Dependency Analysis

Flag heavy dependencies:

  • moment → dayjs or date-fns
  • lodash (full) → lodash-es or individual imports
  • aws-sdk v2 → @aws-sdk/client-* v3

Phase 5: Code Anti-patterns

  • N+1 queries (loop with await)
  • JSON.parse(JSON.stringify()) for clone
  • Missing useMemo/useCallback on expensive operations
  • Sync file ops in request handlers
  • Missing database indexes

Phase 6: Report

# Performance Report

## Bundle
- Total: 1.2MB (gzipped: 380KB)

## Issues Found
🔴 moment.js adds 230KB — replace with dayjs (2KB)
🟡 Full lodash import — use lodash-es

## Recommendations (by impact)
1. Replace moment → dayjs (saves ~228KB)
2. Code-split vendor chunk

Rules

  • Don't make changes — only analyze and report
  • Sort recommendations by estimated impact
  • Include specific numbers (KB saved, ms improved)
  • Suggest alternatives for every heavy dependency flagged