Plugin Development

Plugin Development

This skill provides guidance for creating, structuring, and debugging Claude Code plugins.

When to Use

This skill should be used when:

• Creating a new Claude Code plugin from scratch
• Adding components (commands, agents, skills, hooks, MCP servers) to an existing plugin
• Debugging plugin loading or configuration issues
• Understanding plugin directory structure and manifest format
• Preparing plugins for distribution via marketplaces

Plugin Overview

A Claude Code plugin is a directory containing:

1. .claude-plugin/plugin.json (required) - Plugin manifest with metadata
2. Component directories (optional) - commands/, agents/, skills/, hooks/, .mcp.json
3. Scripts and assets - Supporting files for hooks and utilities

Creating a Plugin

Step 1: Create Directory Structure

my-plugin/
├── .claude-plugin/
│   └── plugin.json       # REQUIRED - manifest
├── commands/             # Slash commands (.md files)
├── agents/               # Subagents (.md files)
├── skills/               # Agent skills (dirs with SKILL.md)
├── hooks/
│   └── hooks.json        # Hook configurations
├── .mcp.json             # MCP server definitions
└── scripts/              # Utility scripts for hooks

Step 2: Create plugin.json

Minimal manifest:

{
  "name": "my-plugin",
  "version": "1.0.0",
  "description": "What this plugin does"
}

Full manifest - see references/manifest-schema.md.

Step 3: Add Components

Commands - Create commands/name.md:

---
description: Brief description for autocomplete
---

# Command Name

Instructions for the command...

Agents - Create agents/name.md:

---
description: What this agent specializes in
capabilities: ["task1", "task2"]
---

# Agent Name

Agent instructions...

Skills - Create skills/name/SKILL.md:

---
name: skill-name
description: What the skill does
---

# Skill Name

Skill instructions...

Hooks - Create hooks/hooks.json or inline in plugin.json:

{
  "hooks": {
    "PostToolUse": [{
      "matcher": "Write|Edit",
      "hooks": [{
        "type": "command",
        "command": "${CLAUDE_PLUGIN_ROOT}/scripts/lint.sh"
      }]
    }]
  }
}

MCP Servers - Create .mcp.json or inline in plugin.json:

{
  "mcpServers": {
    "server-name": {
      "command": "npx",
      "args": ["@company/mcp-server"],
      "cwd": "${CLAUDE_PLUGIN_ROOT}"
    }
  }
}

Publishing as a Marketplace

To make your plugin installable via github: or local: sources, add .claude-plugin/marketplace.json:

{
  "name": "my-marketplace",
  "plugins": [
    {
      "name": "my-skill",
      "description": "What it does",
      "source": "./skills/my-skill"
    },
    {
      "name": "full-plugin",
      "description": "Everything in this plugin",
      "source": "./"
    }
  ]
}

Critical: All source paths must start with ./ (e.g., "./" not ".").

See references/marketplace-schema.md for complete schema.

Critical Rules

1. .claude-plugin/ contains ONLY plugin.json and marketplace.json - All component directories go at plugin root
2. All paths are relative - Must start with ./
3. Use ${CLAUDE_PLUGIN_ROOT} - For absolute paths in hooks/MCP configs
4. Scripts must be executable - Run chmod +x script.sh

Debugging

Run claude --debug to see:

• Which plugins are loading
• Errors in plugin manifests
• Command, agent, and hook registration
• MCP server initialization

Common Issues

Resources

• references/plugin-structure.md - Complete directory layout and file locations
• references/manifest-schema.md - Full plugin.json schema with all fields
• references/marketplace-schema.md - Marketplace.json schema for github/local sources
• references/components.md - Detailed specs for commands, agents, skills, hooks, MCP
• assets/templates/ - Template files for creating new plugins