Plugin Development

Plugin Development Expert

Expert guidance for creating production-ready Claude Code plugins.

Critical Structure Rules

Directory Hierarchy:

~/.claude/plugins/my-plugin/    ← Plugin root
├── .claude-plugin/
│   └── plugin.json            ← Manifest (REQUIRED)
├── commands/
│   └── command-name.md        ← Slash commands
├── skills/
│   └── skill-name/            ← MUST be subdirectory
│       └── SKILL.md           ← MUST be uppercase
└── agents/
    └── agent-name/
        └── AGENT.md

Common Mistakes:

# ❌ WRONG
skills/SKILL.md                # Missing subdirectory
skills/my-skill.md             # Wrong filename
skills/My-Skill/SKILL.md       # CamelCase not allowed

# ✅ CORRECT
skills/my-skill/SKILL.md       # kebab-case subdirectory + SKILL.md

plugin.json Format

Minimum Required:

{
  "name": "my-plugin",
  "description": "Clear description with activation keywords",
  "version": "1.0.0"
}

Full Example:

{
  "name": "my-awesome-plugin",
  "description": "Expert cost optimization for AWS, Azure, GCP. Activates for reduce costs, cloud costs, finops, save money, cost analysis.",
  "version": "1.0.0",
  "author": {
    "name": "Your Name",
    "email": "you@example.com"
  },
  "homepage": "https://github.com/user/my-plugin",
  "repository": "https://github.com/user/my-plugin",
  "license": "MIT",
  "keywords": ["cost", "finops", "aws", "azure", "gcp"]
}

Command Format (Slash Commands)

Header Format (CRITICAL):

# /my-plugin:command-name

Rules:

• MUST start with # /
• Plugin name: kebab-case
• Command name: kebab-case
• NO YAML frontmatter (only skills use YAML)

Full Template:

# /my-plugin:analyze-costs

Analyze cloud costs and provide optimization recommendations.

You are an expert FinOps engineer.

## Your Task

1. Collect cost data
2. Analyze usage patterns
3. Identify optimization opportunities
4. Generate report

### 1. Data Collection

\```bash
aws ce get-cost-and-usage --time-period...
\```

## Example Usage

**User**: "Analyze our AWS costs"

**Response**:
- Pulls Cost Explorer data
- Identifies $5K/month in savings
- Provides implementation plan

## When to Use

- Monthly cost reviews
- Budget overruns
- Pre-purchase planning

Skill Format (Auto-Activating)

YAML Frontmatter (REQUIRED):

---
name: cost-optimization
description: Expert cloud cost optimization for AWS, Azure, GCP. Covers FinOps, reserved instances, spot instances, right-sizing, storage optimization. Activates for reduce costs, save money, cloud costs, aws costs, finops, cost optimization, budget overrun, expensive bill.
---

Activation Keywords:

# ✅ GOOD: Specific, varied keywords
description: Expert Python optimization. Activates for python performance, optimize python code, speed up python, profiling, cProfile, pypy, numba.

# ❌ BAD: Too generic
description: Python expert.

# ❌ BAD: No activation keywords
description: Expert Python optimization covering performance tuning.

Full Template:

---
name: my-skill
description: Expert [domain] covering [topics]. Activates for keyword1, keyword2, phrase3, action4.
---

# Skill Title

You are an expert [role] with deep knowledge of [domain].

## Core Expertise

### 1. Topic Area

Content here...

### 2. Code Examples

\```typescript
// Working examples
\```

## Best Practices

- Practice 1
- Practice 2

You are ready to help with [domain]!

Agent Format (Sub-Agents)

File Location:

agents/agent-name/AGENT.md

Template:

---
name: specialist-agent
description: Specialized agent for [specific task]
---

# Agent Title

You are a specialized agent for [purpose].

## Capabilities

1. Capability 1
2. Capability 2

## Workflow

1. Analyze input
2. Execute specialized task
3. Return results

Invocation:

Task({
  subagent_type: "plugin-name:folder-name:yaml-name",
  prompt: "Task description"
});

// Example
Task({
  subagent_type: "my-plugin:specialist-agent:specialist-agent",
  prompt: "Analyze this code for security vulnerabilities"
});

Testing Workflow

1. Install Plugin:

cp -r my-plugin ~/.claude/plugins/
# OR
claude plugin add github:username/my-plugin

2. Restart Claude Code:

# Required after:
- Adding new plugin
- Modifying plugin.json
- Adding/removing commands
- Changing YAML frontmatter

3. Test Commands:

# Type "/" in Claude Code
# Verify command appears: /my-plugin:command-name
# Execute command
# Verify behavior

4. Test Skills:

# Ask trigger question: "How do I reduce costs?"
# Verify skill activates
# Check response uses skill knowledge

5. Check Logs:

tail -f ~/.claude/logs/claude.log | grep my-plugin

# Expected:
# ✅ "Loaded plugin: my-plugin"
# ✅ "Registered command: /my-plugin:analyze"
# ✅ "Registered skill: cost-optimization"

# Errors:
# ❌ "Failed to parse plugin.json"
# ❌ "YAML parsing error in SKILL.md"
# ❌ "Command header malformed"

Common Issues

Issue: Skill not activating

Checklist:
1. ✅ YAML frontmatter present? (---...---)
2. ✅ Activation keywords in description?
3. ✅ SKILL.md in subdirectory? (skills/name/SKILL.md)
4. ✅ File named SKILL.md (uppercase)?
5. ✅ Claude Code restarted?

Issue: Command not found

Checklist:
1. ✅ Header format: # /plugin-name:command-name
2. ✅ File in commands/ directory?
3. ✅ Plugin name matches plugin.json?
4. ✅ Claude Code restarted?

Issue: YAML parsing error

Common causes:
- Unclosed quotes: description: "Missing end
- Invalid characters: name: my_skill (use hyphens)
- Missing closing ---
- Incorrect indentation

Best Practices

Naming:

• Plugin: my-awesome-plugin (kebab-case)
• Commands: analyze-costs (kebab-case)
• Skills: cost-optimization (kebab-case)
• NO underscores, NO CamelCase

Activation Keywords:

• Include 5-10 trigger keywords
• Mix specific terms and common phrases
• Think about what users will ask
• Test with real questions

Documentation:

• Clear "Your Task" section
• Code examples with syntax highlighting
• "Example Usage" section
• "When to Use" section

Performance:

• Keep SKILL.md under 50KB
• Optimize command prompts
• Avoid expensive operations

Create production-ready Claude Code plugins!