# Agent Development

> This skill should be used when the user asks to "create an agent", "add an agent", "write a subagent", "agent frontmatter", "when to use description", "agent examples", "agent tools", "agent colors", "autonomous agent", or needs guidance on agent structure, system prompts, triggering conditions, or agent development best practices for Claude Code plugins.

- Skill: `dreydrey9000/agent-development` (Agent Skill, multi-file: 10 files)
- Install (CLI): `npx skillmds@latest add dreydrey9000/agent-development`
- Raw SKILL.md: https://api.skillmd.com/api/skills/dreydrey9000/agent-development/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: Dreydrey9000 (https://skillmd.com/u/dreydrey9000)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/dreydrey9000/agent-development

---


# Agent Development for Claude Code Plugins

## Overview

Agents are autonomous subprocesses that handle complex, multi-step tasks independently. Understanding agent structure, triggering conditions, and system prompt design enables creating powerful autonomous capabilities.

**Key concepts:**
- Agents are FOR autonomous work, commands are FOR user-initiated actions
- Markdown file format with YAML frontmatter
- Triggering via description field with examples
- System prompt defines agent behavior
- Model and color customization

## Agent File Structure

## Frontmatter Fields

### model (required)

Which model the agent should use.

**Options:**
- `inherit` - Use same model as parent (recommended)
- `sonnet` - Claude Sonnet (balanced)
- `opus` - Claude Opus (most capable, expensive)
- `haiku` - Claude Haiku (fast, cheap)

**Recommendation:** Use `inherit` unless agent needs specific model capabilities.

### color (required)

Visual identifier for agent in UI.

**Options:** `blue`, `cyan`, `green`, `yellow`, `magenta`, `red`

**Guidelines:**
- Choose distinct colors for different agents in same plugin
- Use consistent colors for similar agent types
- Blue/cyan: Analysis, review
- Green: Success-oriented tasks
- Yellow: Caution, validation
- Red: Critical, security
- Magenta: Creative, generation

## System Prompt Design

The markdown body becomes the agent's system prompt. Write in second person, addressing the agent directly.

## Creating Agents

### Method 2: Manual Creation

1. Choose agent identifier (3-50 chars, lowercase, hyphens)
2. Write description with examples
3. Select model (usually `inherit`)
4. Choose color for visual identification
5. Define tools (if restricting access)
6. Write system prompt with structure above
7. Save as `agents/agent-name.md`

## Validation Rules

### Identifier Validation

```
✅ Valid: code-reviewer, test-gen, api-analyzer-v2
❌ Invalid: ag (too short), -start (starts with hyphen), my_agent (underscore)
```

**Rules:**
- 3-50 characters
- Lowercase letters, numbers, hyphens only
- Must start and end with alphanumeric
- No underscores, spaces, or special characters

### Description Validation

**Length:** 10-5,000 characters
**Must include:** Triggering conditions and examples
**Best:** 200-1,000 characters with 2-4 examples

### System Prompt Validation

**Length:** 20-10,000 characters
**Best:** 500-3,000 characters
**Structure:** Clear responsibilities, process, output format

## Agent Organization

### Plugin Agents Directory

```
plugin-name/
└── agents/
    ├── analyzer.md
    ├── reviewer.md
    └── generator.md
```

All `.md` files in `agents/` are auto-discovered.

### Namespacing

Agents are namespaced automatically:
- Single plugin: `agent-name`
- With subdirectories: `plugin:subdir:agent-name`

## Testing Agents

### Test Triggering

Create test scenarios to verify agent triggers correctly:

1. Write agent with specific triggering examples
2. Use similar phrasing to examples in test
3. Check Claude loads the agent
4. Verify agent provides expected functionality

### Test System Prompt

Ensure system prompt is complete:

1. Give agent typical task
2. Check it follows process steps
3. Verify output format is correct
4. Test edge cases mentioned in prompt
5. Confirm quality standards are met

### Frontmatter Fields Summary

| Field | Required | Format | Example |
|-------|----------|--------|---------|
| name | Yes | lowercase-hyphens | code-reviewer |
| description | Yes | Text + examples | Use when... <example>... |
| model | Yes | inherit/sonnet/opus/haiku | inherit |
| color | Yes | Color name | blue |
| tools | No | Array of tool names | ["Read", "Grep"] |

### Best Practices

**DO:**
- ✅ Include 2-4 concrete examples in description
- ✅ Write specific triggering conditions
- ✅ Use `inherit` for model unless specific need
- ✅ Choose appropriate tools (least privilege)
- ✅ Write clear, structured system prompts
- ✅ Test agent triggering thoroughly

**DON'T:**
- ❌ Use generic descriptions without examples
- ❌ Omit triggering conditions
- ❌ Give all agents same color
- ❌ Grant unnecessary tool access
- ❌ Write vague system prompts
- ❌ Skip testing

## Additional Resources

### Example Files

Working examples in `examples/`:

- **`agent-creation-prompt.md`** - AI-assisted agent generation template
- **`complete-agent-examples.md`** - Full agent examples for different use cases

### Utility Scripts

Development tools in `scripts/`:

- **`validate-agent.sh`** - Validate agent file structure
- **`test-agent-trigger.sh`** - Test if agent triggers correctly


## Full Specification

Complete details, decision trees, protocols, and implementation specs: [references/full-details.md](references/full-details.md)