bundle-analyze

name	bundle-analyze
description	JavaScript bundle analysis. Checks bundle sizes, tree-shaking effectiveness, duplicate dependencies, and chunk splitting.

bundle-analyze - Bundle Size Analysis

Analyzes JavaScript bundles for size issues, duplicate dependencies, and optimization opportunities.

Input Schema

{
  "project_dir": "/path/to/project",
  "build_dir": "dist/",
  "budgets": {
    "total": "500KB",
    "main": "200KB",
    "vendor": "300KB"
  },
  "checks": ["size", "duplicates", "tree_shaking"]
}

Instructions

1. Measure Bundle Sizes

# Get file sizes
du -h dist/*.js

# Get gzipped sizes
gzip -c dist/main.js | wc -c

2. Analyze with source-map-explorer

# Generate bundle analysis
npx source-map-explorer dist/main.js --json > bundle-analysis.json

3. Check for Duplicates

# Find duplicate packages
npx depcheck --json | jq '.missing, .dependencies'

# Check bundle for duplicates
npx webpack-bundle-analyzer dist/stats.json --mode static

4. Verify Tree Shaking

// Check if unused exports are removed
// Look for side-effect-free imports that should be eliminated

Output Format

{
  "skill": "bundle-analyze",
  "status": "pass|warning|fail",
  "bundles": {
    "total": {
      "raw": "423KB",
      "gzip": "142KB",
      "budget": "500KB",
      "passed": true
    },
    "main": {
      "raw": "156KB",
      "gzip": "52KB",
      "budget": "200KB",
      "passed": true
    },
    "vendor": {
      "raw": "267KB",
      "gzip": "90KB",
      "budget": "300KB",
      "passed": true
    }
  },
  "duplicates": [
    {
      "package": "lodash",
      "versions": ["4.17.21", "4.17.19"],
      "size_impact": "24KB",
      "suggestion": "Dedupe to single version"
    }
  ],
  "large_modules": [
    {
      "module": "moment",
      "size": "67KB",
      "suggestion": "Replace with date-fns or dayjs"
    }
  ],
  "tree_shaking": {
    "effective": true,
    "unused_exports": []
  },
  "suggestions": [
    "Consider lazy loading for route /dashboard",
    "Replace moment.js with lighter alternative"
  ],
  "errors": [],
  "next_action": "proceed|optimize"
}

Budget Thresholds

Bundle Type	Warning	Fail
Total	>400KB	>600KB
Main	>150KB	>250KB
Vendor	>250KB	>400KB
Per-route chunk	>100KB	>200KB

Checks Performed

Check	What it Validates
size	Bundle sizes within budget
duplicates	No duplicate package versions
tree_shaking	Unused code eliminated
chunks	Proper code splitting
sourcemaps	Source maps generated

Decision Logic

Any bundle exceeds fail threshold?
    YES → status: "fail", next_action: "optimize"

Any bundle exceeds warning threshold?
    YES → status: "warning", suggestions populated

Duplicate packages found?
    YES → Add to suggestions

All within budget?
    YES → status: "pass", next_action: "proceed"

Usage Examples

Full bundle analysis:

{
  "project_dir": "/projects/react-app",
  "build_dir": "build/",
  "budgets": {
    "total": "500KB",
    "main": "200KB",
    "vendor": "300KB"
  },
  "checks": ["size", "duplicates", "tree_shaking"]
}

Quick size check:

{
  "project_dir": "/projects/react-app",
  "build_dir": "dist/",
  "budgets": {
    "total": "500KB"
  },
  "checks": ["size"]
}

Duplicate detection:

{
  "project_dir": "/projects/react-app",
  "build_dir": "dist/",
  "checks": ["duplicates"]
}

Token Efficiency

• Uses existing build output
• JSON-based analysis
• ~5-15 second execution
• Returns actionable suggestions