Skill Porter - Cross-Platform Skill Converter

This skill automates the conversion between Claude Code skills and Gemini CLI extensions, enabling true cross-platform AI tool development.

Core Capabilities

Bidirectional Conversion

Convert skills and extensions between platforms while preserving functionality:

Example requests:

• "Convert this Claude skill to work with Gemini CLI"
• "Make my Gemini extension compatible with Claude Code"
• "Create a universal version of this skill that works on both platforms"
• "Port the database-helper skill to Gemini"

Smart Platform Detection

Automatically analyzes directory structure to determine source platform:

Detection criteria:

• Claude: Presence of SKILL.md with YAML frontmatter or .claude-plugin/marketplace.json
• Gemini: Presence of gemini-extension.json or GEMINI.md context file
• Universal: Has both platform configurations

Example requests:

• "What platform is this skill built for?"
• "Analyze this extension and tell me what needs to be converted"
• "Is this a Claude skill or Gemini extension?"

Metadata Transformation

Intelligently converts between platform-specific formats:

Conversions handled:

• YAML frontmatter ↔ JSON manifest
• allowed-tools (whitelist) ↔ excludeTools (blacklist)
• Environment variables ↔ settings schema
• MCP server configuration paths
• Platform-specific documentation formats

Example requests:

• "Convert the metadata from this Claude skill to Gemini format"
• "Transform the allowed-tools list to Gemini's exclude pattern"
• "Generate a settings schema from these environment variables"

MCP Server Preservation

Maintains Model Context Protocol server configurations across platforms:

Example requests:

• "Ensure the MCP server config works on both platforms"
• "Update the MCP server paths for Gemini's ${extensionPath} variable"
• "Validate that the MCP configuration is compatible"

Validation & Quality Checks

Ensures converted output meets platform requirements:

Validation checks:

• Required files present (SKILL.md, gemini-extension.json, etc.)
• Valid YAML/JSON syntax
• Correct frontmatter structure
• MCP server paths resolve correctly
• Tool restrictions are valid
• Settings schema is complete

Example requests:

• "Validate this converted skill"
• "Check if this Gemini extension meets all requirements"
• "Is this conversion ready to install?"

Conversion Process

When you request a conversion, I will:

1. Analyze the source directory structure
2. Detect which platform it's built for
3. Extract metadata, MCP configuration, and documentation
4. Transform the data to target platform format
5. Generate required files for target platform
6. Validate output meets all requirements
7. Report what was converted and any manual steps needed

Platform Differences Handled

File Structure

• Claude: SKILL.md + .claude-plugin/marketplace.json
• Gemini: GEMINI.md + gemini-extension.json
• Universal: Both sets of files + shared documentation

Metadata Format

• Claude: YAML frontmatter in SKILL.md
• Gemini: JSON manifest file
• Conversion: Bidirectional YAML ↔ JSON transformation

Tool Restrictions

• Claude: allowed-tools (whitelist - only listed tools permitted)
• Gemini: excludeTools (blacklist - listed patterns blocked)
• Conversion: Logic inversion with intelligent mapping

Configuration

• Claude: Environment variables (user sets before running)
• Gemini: Settings schema (prompted during installation)
• Conversion: Infer schema from env vars or generate env var docs

MCP Server Paths

• Claude: Relative paths from skill directory
• Gemini: Uses ${extensionPath} variable substitution
• Conversion: Automatic path transformation

Usage Examples

Convert Claude Skill to Gemini

User: "I have a Claude skill at ./database-helper. Convert it to Gemini."
Claude: I'll analyze the skill and convert it to Gemini format...
- Detected Claude skill (found SKILL.md with frontmatter)
- Extracted metadata and MCP configuration
- Generated gemini-extension.json and GEMINI.md
- Transformed allowed-tools to excludeTools
- Created settings schema from environment variables
✓ Conversion complete! Ready to install with: gemini extensions install ./database-helper

Convert Gemini Extension to Claude

User: "Port my Gemini extension to Claude Code"
Claude: I'll convert this Gemini extension to a Claude skill...
- Detected Gemini extension (found gemini-extension.json)
- Extracted manifest and context file
- Generated SKILL.md with YAML frontmatter
- Created .claude-plugin/marketplace.json
- Converted excludeTools to allowed-tools
✓ Conversion complete! Install with: cp -r ./extension ~/.claude/skills/

Create Universal Extension

User: "Make this skill work on both platforms"
Claude: I'll create a universal extension structure...
- Analyzing current configuration
- Generating both Claude and Gemini files
- Moving shared content to shared/ directory
- Updating MCP server paths for both platforms
✓ Universal extension created! Works with both Claude Code and Gemini CLI

Advanced Features

Pull Request Generation

Create a PR to add dual-platform support to the parent repository:

Example requests:

• "Convert this skill and create a PR to add Gemini support"
• "Generate a pull request with the universal version"

Fork and Dual Setup

Create a fork with both platform configurations:

Example requests:

• "Fork this repo and set it up for both platforms"
• "Create a dual-platform fork I can use with both CLIs"

Validation Only

Check compatibility without converting:

Example requests:

• "Validate this skill's conversion to Gemini"
• "Check if this extension can be ported to Claude"
• "What needs to change to make this universal?"

Configuration

This skill operates directly on filesystem directories and doesn't require external configuration. It uses:

• File system access to read and write skill/extension files
• Git operations for PR and fork features
• GitHub CLI (gh) for repository operations

Safety Features

• Non-destructive: Creates new files, doesn't modify source unless explicitly requested
• Validation: Checks output before completion
• Reporting: Clear summary of changes made
• Rollback friendly: All changes are standard file operations

Limitations

Some aspects may require manual review:

• Custom slash commands (platform-specific syntax)
• Complex MCP server configurations with multiple servers
• Platform-specific scripts that don't translate directly
• Edge cases in tool restriction mapping

These will be flagged in the conversion report.

Technical Details

Tool Restriction Conversion

Claude → Gemini (Whitelist → Blacklist):

• Analyze allowed-tools list
• Generate exclude patterns for all other tools
• Special handling for wildcard permissions

Gemini → Claude (Blacklist → Whitelist):

• List all available tools
• Remove excluded tools
• Generate allowed-tools list

Settings Inference

When converting Claude → Gemini, environment variables in MCP config become settings:

// MCP env var
"env": { "DB_HOST": "${DB_HOST}" }

// Becomes Gemini setting
"settings": [{
  "name": "DB_HOST",
  "description": "Database host",
  "default": "localhost"
}]

Path Transformation

Claude uses relative paths, Gemini uses variables:

// Claude
"args": ["mcp-server/index.js"]

// Gemini
"args": ["${extensionPath}/mcp-server/index.js"]

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For implementation details, see the repository at https://github.com/jduncan-rva/skill-porter