Browserslist Skill

Purpose

Generate Browserslist configuration to define supported browsers for CSS autoprefixing and JavaScript transpilation.

🚨 MANDATORY FILE COUNT

This skill MUST create exactly 1 file:

• .browserslistrc

  (preferred format)

🔍 BEFORE GENERATING

Research current Browserslist standards to ensure accuracy:

1. Check Browserslist documentation for latest query syntax
2. Verify recommended browser targets for modern web applications
3. Check if any queries have been deprecated or new ones added
4. Verify file format options (standalone file vs package.json)

Output

Create the file:

.browserslistrc

Supported Formats (in order of preference):

1. .browserslistrc

   (preferred - standalone file)

2. browserslist

   field in

   package.json

3. .browserslistrc.json

   (JSON format)

Example Configuration (As of December 2025 - May be outdated)

⚠️ DEPRECATION WARNING: This example uses December 2025 standards. Always verify current Browserslist query syntax and recommended targets before using.

Preferred:

.browserslistrc

> 1%
last 2 versions
not dead
not ie 11

Alternative: package.json field

{
  "browserslist": [
    "> 1%",
    "last 2 versions",
    "not dead",
    "not ie 11"
  ]
}

Query Explanations:

• > 1%

  - Browsers with >1% global usage

• last 2 versions

  - Last 2 versions of all major browsers

• not dead

  - Exclude browsers without official support

• not ie 11

  - Explicitly exclude Internet Explorer 11

Execution Checklist

• Research current Browserslist query syntax and standards
• Check if recommended browser targets have changed
• Verify query syntax hasn't been deprecated
• Create

  .browserslistrc

  file with appropriate queries
• Verify file format follows current standards

🛑 BLOCKING VALIDATION CHECKPOINT

STOP! Before proceeding to the next skill, verify:

Automated Verification

Run this command to verify the file exists:

if [ -f ".browserslistrc" ] || grep -q "browserslist" package.json 2>/dev/null || [ -f ".browserslistrc.json" ]; then
  echo "✓ Browserslist configuration found"
  if [ -f ".browserslistrc" ]; then
    echo "✓ Using .browserslistrc (preferred format)"
  fi
else
  echo "✗ Browserslist configuration missing"
  exit 1
fi

Manual Verification

1. ✓

   .browserslistrc

   exists at project root (or browserslist in package.json)
2. ✓ File contains browser targeting queries
3. ✓ Queries follow current Browserslist syntax standards
4. ✓ Configuration balances modern features with browser support

If Validation Fails

DO NOT PROCEED to the next skill. Create the missing file immediately.

Notes

• Targets browsers with >1% market share
• Supports last 2 versions of all major browsers
• Excludes browsers without official support or security updates (dead browsers)
• Explicitly excludes Internet Explorer 11
• Used by Autoprefixer, Babel, PostCSS, and other build tools
• Helps optimize bundle size by not supporting outdated browsers
• Ensures modern browser features can be used with appropriate polyfills
• Query syntax evolves - New queries may be added, old ones deprecated
• Always verify current standards - Browser landscape changes over time
• Can test queries at: https://browsersl.ist/