plugin-expert

Plugin Development Guide

Quick Reference

Component	Location	Required
Plugin manifest	.claude-plugin/plugin.json	Yes
Commands	commands/*.md	No (auto-discovered)
Agents	agents/*.md	No (auto-discovered)
Skills	skills/*/SKILL.md	No (auto-discovered)
Hooks	hooks/hooks.json	No
MCP Servers	.mcp.json	No

Task	Action
Create plugin	Ask: "Create a plugin for X"
Validate plugin	Run: /validate-plugin
Install from marketplace	/plugin marketplace add user/repo then /plugin install name@user

Critical Rules

Directory Structure

plugin-name/
├── .claude-plugin/
│   └── plugin.json          # MUST be inside .claude-plugin/
├── agents/
│   └── domain-expert.md
├── commands/
├── skills/
│   └── skill-name/
│       ├── SKILL.md
│       ├── references/
│       └── examples/
└── README.md

Plugin.json Schema

{
  "name": "plugin-name",
  "version": "1.0.0",
  "description": "Complete [domain] expertise. PROACTIVELY activate for: (1) ...",
  "author": {
    "name": "Author Name",
    "email": "[email protected]"
  },
  "license": "MIT",
  "keywords": ["keyword1", "keyword2"]
}

Validation Rules:

• author MUST be an object { "name": "..." } - NOT a string
• version MUST be a string "1.0.0" - NOT a number
• keywords MUST be an array ["word1", "word2"] - NOT a string
• Do NOT include agents, skills, slashCommands - these are auto-discovered

YAML Frontmatter (REQUIRED)

ALL markdown files in agents/, commands/, skills/ MUST begin with frontmatter:

---
description: Brief description of what this component does
---

# Content...

Without frontmatter, components will NOT load.

Plugin Design Philosophy (2025)

Agent-First Design

• Primary interface: ONE expert agent named {domain}-expert
• Minimal commands: Only 0-2 for automation workflows
• Why: Users want conversational interaction, not command menus

Naming Standard:

• docker-master → agent named docker-expert
• terraform-master → agent named terraform-expert

Progressive Disclosure for Skills

Skills use three-tier loading:

1. Frontmatter - Loaded at startup for triggering
2. SKILL.md body - Loaded when skill activates
3. references/ - Loaded only when specific detail needed

This enables unbounded capacity without context bloat.

Creating a Plugin

Step 1: Detect Repository Context

Before creating files, check:

# Check if in marketplace repo
if [[ -f .claude-plugin/marketplace.json ]]; then
    PLUGIN_DIR="plugins/PLUGIN_NAME"
else
    PLUGIN_DIR="PLUGIN_NAME"
fi

# Get author from git config
AUTHOR_NAME=$(git config user.name)
AUTHOR_EMAIL=$(git config user.email)

Step 2: Create Structure

mkdir -p $PLUGIN_DIR/.claude-plugin
mkdir -p $PLUGIN_DIR/agents
mkdir -p $PLUGIN_DIR/skills/domain-knowledge

Step 3: Create Files

1. plugin.json - Manifest with metadata
2. agents/domain-expert.md - Primary expert agent
3. skills/domain-knowledge/SKILL.md - Core knowledge
4. README.md - Documentation

Step 4 (conditional): Attribution manifest

If the plugin ships any vendored, derived, or licensed third-party content, create NOTICES.md at the plugin root before registering in the marketplace. Treat it as a first-class shipping artifact alongside plugin.json and README.md, not as doc polish. See references/publishing-guide.md ("Licensed / Vendored / Derived Content" checklist) for the structural integrity, license-text-preservation, and cross-reference requirements.

If the plugin contains no third-party content, skip this step.

Step 5: Register in Marketplace

CRITICAL: If .claude-plugin/marketplace.json exists at repo root, you MUST add the plugin:

{
  "plugins": [
    {
      "name": "plugin-name",
      "source": "./plugins/plugin-name",
      "description": "Same as plugin.json description",
      "version": "1.0.0",
      "author": { "name": "Author" },
      "keywords": ["same", "as", "plugin.json"]
    }
  ]
}

Component Types

Commands

User-initiated slash commands in commands/*.md:

---
description: What this command does
---

# Command Name

Instructions for Claude to execute...

Agents

Autonomous subagents in agents/*.md:

---
name: agent-name
description: |
  Brief role summary. PROACTIVELY activate for: (1) trigger, (2) trigger, ..., (N) trigger. Provides: capability list.

  # Optional. Include 3-5 <example> blocks ONLY when the agent body
  # exceeds 2,500 words. Lean orchestrators omit them by design.
  # See agent-development "Example-block requirement by agent body size".
model: inherit
color: blue
---

System prompt for agent...

Skills

Dynamic knowledge in skills/skill-name/SKILL.md:

---
name: skill-name
description: When to use this skill...
---

# Skill content with progressive disclosure...

Hooks

Event automation in hooks/hooks.json:

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

Events: PreToolUse, PostToolUse, SessionStart, SessionEnd, UserPromptSubmit, PreCompact, Notification, Stop, SubagentStop

Best Practices

Naming Conventions

• Plugins: kebab-case (e.g., code-review-helper)
• Commands: verb-based (e.g., review-pr, run-tests)
• Agents: role-based (e.g., code-reviewer, test-generator)
• Skills: topic-based (e.g., api-design, error-handling)

Portability

Use ${CLAUDE_PLUGIN_ROOT} for all internal paths:

"command": "${CLAUDE_PLUGIN_ROOT}/scripts/run.sh"

Never use hardcoded absolute paths.

Platform Notes

• Windows: Use GitHub marketplace installation (local paths may fail)
• Git Bash/MinGW: Detect with $MSYSTEM, use GitHub method
• Mac/Linux: All installation methods work

Troubleshooting

Issue	Solution
Plugin not loading	Check plugin.json is in .claude-plugin/
Commands missing	Verify frontmatter has description field
Agent not triggering	Check description has PROACTIVELY activate for: enumeration. Add 3-5 <example> blocks only if agent body > 2,500 words — see agent-development SKILL.md "Example-block requirement by agent body size". Lean orchestrators are exempt.
Marketplace not found	Ensure repo is public, check path in marketplace.json

Additional Resources

For detailed information, see:

• references/manifest-reference.md - Complete plugin.json fields
• references/component-patterns.md - Advanced component patterns
• references/publishing-guide.md - Marketplace publishing details
• examples/minimal-plugin.md - Simplest working plugin
• examples/full-plugin.md - Complete plugin with all features