Code Formatter Skill

Purpose

Automatically format and lint code across multiple languages, enforcing consistent style and fixing common issues without manual intervention.

When to Use

• Before committing code
• During PR preparation
• After code generation
• When enforcing team standards
• Batch formatting of legacy code

Supported Languages

JavaScript/TypeScript

• Formatter: Prettier
• Linter: ESLint
• Auto-fix: Import sorting, semicolons, quotes

Python

• Formatter: Black
• Linter: isort, autopep8
• Auto-fix: Import sorting, line length, indentation

Go

• Formatter: gofmt, goimports
• Auto-fix: Import organization, formatting

Rust

• Formatter: rustfmt
• Auto-fix: Clippy suggestions

Other Languages

• JSON: Prettier
• YAML: Prettier
• Markdown: Prettier
• CSS/SCSS: Prettier
• HTML: Prettier

Operations

1. Detect Language and Style

• Auto-detect language from file extension
• Load project-specific configuration
• Identify style guide (Standard, Airbnb, Google, etc.)

2. Format Code

• Apply formatter rules
• Preserve semantics (no behavior changes)
• Handle edge cases (strings, comments, etc.)

3. Fix Linting Issues

• Run linter with auto-fix enabled
• Apply safe automated fixes
• Report remaining manual fixes needed

4. Generate Report

• List files modified
• Show statistics (lines changed, issues fixed)
• Output diff for review

Scripts

main.py

# Execute formatting
python scripts/main.py format <file_or_dir> [--language=auto] [--check-only]

# Check formatting without modifying
python scripts/main.py check <file_or_dir>

# Show supported languages
python scripts/main.py languages

# Generate configuration
python scripts/main.py init --language=javascript

Language-Specific Formatters

• format_javascript.js - ESLint + Prettier
• format_python.py - Black + isort
• format_go.sh - gofmt + goimports
• format_rust.sh - rustfmt + clippy

Configuration

Project-Specific Settings

The Skill checks for configuration in this order:

1. .prettierrc, .eslintrc (JavaScript)
2. pyproject.toml, setup.cfg (Python)
3. .rustfmt.toml (Rust)
4. Memory-stored preferences
5. Sensible defaults

Memory Integration

Stores formatting preferences:

{
  "topic": "code-formatter-preferences",
  "scope": "repository",
  "value": {
    "javascript": {
      "formatter": "prettier",
      "semi": false,
      "singleQuote": true,
      "tabWidth": 2
    },
    "python": {
      "formatter": "black",
      "lineLength": 88,
      "importSorter": "isort"
    }
  }
}

Integration Points

With PR Author/Reviewer Skill

• Auto-format before creating PR
• Include formatting changes in PR description
• Validate formatting in PR checks

With Memory Hygiene Skill

• Track formatting statistics
• Record team preferences
• Monitor adoption rates

With Test-First Change Skill

• Format test files
• Maintain consistent test style
• Preserve test semantics

Examples

Format Single File

# Auto-detect language and format
python scripts/main.py format src/index.js

# Output:
# ✅ Formatted src/index.js (JavaScript)
# - Fixed 3 ESLint issues
# - Reformatted 127 lines

Format Directory

# Format all files in directory
python scripts/main.py format src/ --language=auto

# Output:
# ✅ Formatted 47 files
# - JavaScript: 23 files
# - TypeScript: 18 files
# - JSON: 6 files

Check Only Mode

# Check without modifying (CI/CD)
python scripts/main.py check src/

# Output:
# ❌ 3 files need formatting:
# - src/app.js
# - src/utils.js
# - src/config.json

Initialize Configuration

# Create project configuration
python scripts/main.py init --language=javascript

# Output:
# ✅ Created .prettierrc
# ✅ Created .eslintrc.json
# Configuration stored in memory

Token Economics

Without Skill (Agent formatting):

• Parse file: 2,000 tokens
• Analyze style: 3,000 tokens
• Generate formatted code: 5,000 tokens
• Explain changes: 2,000 tokens
• Total: 12,000 tokens

With Skill (Code execution):

• Metadata: 50 tokens
• SKILL.md: 350 tokens
• Script execution: 0 tokens (returns result)
• Result parsing: 100 tokens
• Total: 500 tokens

Savings: 95.8% (11,500 tokens saved per operation)

Success Metrics

Performance

• Formatting time: <1 second per file
• Batch processing: >100 files/minute
• Memory usage: <100MB

Quality

• Code consistency: 100%
• Semantic preservation: 100%
• False positives: <1%

Adoption

• Developer usage: >90%
• CI/CD integration: 100% of projects
• Satisfaction rating: >4.5/5

Safety Checks

Before formatting:

1. ✅ Backup original file (in-memory)
2. ✅ Validate syntax (no broken code)
3. ✅ Preserve file permissions
4. ✅ Maintain git history

After formatting:

1. ✅ Verify file integrity
2. ✅ Check for unintended changes
3. ✅ Run syntax validation
4. ✅ Generate diff for review

Error Handling

Syntax Errors

❌ Cannot format src/broken.js: Syntax error at line 42
Recommendation: Fix syntax errors before formatting

Missing Dependencies

⚠️  Prettier not found. Install with: npm install -g prettier
Falling back to basic formatting

Configuration Conflicts

⚠️  Multiple configurations found (.prettierrc and package.json)
Using .prettierrc (higher priority)

Limitations

• Does not fix logic errors
• Cannot resolve complex linting issues requiring human judgment
• May conflict with custom editor settings
• Large files (>10,000 lines) may be slow

References

See references/ for:

• style-guides.md - Popular style guides by language
• configuration-examples/ - Sample configs for common setups
• troubleshooting.md - Common issues and solutions

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Code Formatter Skill v1.0.0 - Write code once, format it everywhere