---
name: kit-agent-development
description: (ePost) 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.
disable-model-invocation: true
metadata:
  keywords:
    - agent-development
    - create-agent
    - system-prompt
    - agent-frontmatter
  agent-affinity:
    - epost-fullstack-developer
  platforms:
    - all
  connections:
    enhances: [kit-agents]
---

# 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

### Complete Format

```markdown
---
name: agent-identifier
description: Use this agent when [triggering conditions]. Examples:

<example>
Context: [Situation description]
user: "[User request]"
assistant: "[How assistant should respond and use this agent]"
<commentary>
[Why this agent should be triggered]
</commentary>
</example>

<example>
[Additional example...]
</example>

model: inherit
color: blue
tools: ["Read", "Write", "Grep"]
"
---

You are [agent role description]...

**Your Core Responsibilities:**
1. [Responsibility 1]
2. [Responsibility 2]

**Analysis Process:**
[Step-by-step workflow]

**Output Format:**
[What to return]
```

## Frontmatter Fields

### name (required)

Agent identifier used for namespacing and invocation.

**Format:** lowercase, numbers, hyphens only
**Length:** 3-50 characters
**Pattern:** Must start and end with alphanumeric

**Good examples:**
- `code-reviewer`
- `test-generator`
- `api-docs-writer`
- `security-analyzer`

**Bad examples:**
- `helper` (too generic)
- `-agent-` (starts/ends with hyphen)
- `my_agent` (underscores not allowed)
- `ag` (too short, < 3 chars)

### description (required)

Defines when Claude should trigger this agent. **This is the most critical field.**

**Must include:**
1. Triggering conditions ("Use this agent when...")
2. Multiple `<example>` blocks showing usage
3. Context, user request, and assistant response in each example
4. `<commentary>` explaining why agent triggers

**Format:**
```
Use this agent when [conditions]. Examples:

<example>
Context: [Scenario description]
user: "[What user says]"
assistant: "[How Claude should respond]"
<commentary>
[Why this agent is appropriate]
</commentary>
</example>

[More examples...]
```

**Best practices:**
- Include 2-4 concrete examples
- Show proactive and reactive triggering
- Cover different phrasings of same intent
- Explain reasoning in commentary
- Be specific about when NOT to use the agent

### 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

### tools (optional)

Restrict agent to specific tools.

**Format:** Array of tool names

```yaml
tools: ["Read", "Write", "Grep", "Bash"]
```

**Default:** If omitted, agent has access to all tools

**Best practice:** Limit tools to minimum needed (principle of least privilege)

**Common tool sets:**
- Read-only analysis: `["Read", "Grep", "Glob"]`
- Code generation: `["Read", "Write", "Grep"]`
- Testing: `["Read", "Bash", "Grep"]`
- Full access: Omit field or use `["*"]`

## System Prompt Design

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

### Structure

**Standard template:**
```markdown
You are [role] specializing in [domain].

**Your Core Responsibilities:**
1. [Primary responsibility]
2. [Secondary responsibility]
3. [Additional responsibilities...]

**Analysis Process:**
1. [Step one]
2. [Step two]
3. [Step three]
[...]

**Quality Standards:**
- [Standard 1]
- [Standard 2]

**Output Format:**
Provide results in this format:
- [What to include]
- [How to structure]

**Edge Cases:**
Handle these situations:
- [Edge case 1]: [How to handle]
- [Edge case 2]: [How to handle]
```

### Best Practices

✅ **DO:**
- Write in second person ("You are...", "You will...")
- Be specific about responsibilities
- Provide step-by-step process
- Define output format
- Include quality standards
- Address edge cases
- Keep under 10,000 characters

❌ **DON'T:**
- Write in first person ("I am...", "I will...")
- Be vague or generic
- Omit process steps
- Leave output format undefined
- Skip quality guidance
- Ignore error cases

## Creating Agents

See `references/agent-creation-guide.md` for:
- AI-assisted generation prompt template
- Manual creation steps
- Validation rules (identifier, description, system prompt)
- Testing workflows
- Agent organization and namespacing

## Quick Reference

### Minimal Agent

```markdown
"
---
name: simple-agent
description: Use this agent when... Examples: <example>...</example>
model: inherit
color: blue
---

You are an agent that [does X].

Process:
1. [Step 1]
2. [Step 2]

Output: [What to provide]
```

### Ecosystem Fields (ePost Agent Kit)

When creating agents for the ePost agent kit, these additional fields configure agent behavior:

**`skills`** — Array of skill IDs the agent should load. Use bracket notation: `skills: [core, debugging]`. Most agents include `core` as the first skill. Read-only agents (researcher, reviewer) may omit implementation skills.

**`memory`** — Controls agent memory scope. Use `project` for agents that need cross-session context. Use `session` for agents with ephemeral tasks.

**`permissionMode`** — Controls what actions the agent can take without user confirmation:
- `default` — Standard permission prompts (most agents)
- `acceptEdits` — Auto-accept file edits (implementers, developers)
- `plan` — Read-only exploration, no writes (architects, researchers, reviewers)
- `bypassPermissions` — Full autonomy (use with caution)

**`disallowedTools`** — Explicitly prevent agent from using specific tools. Useful for read-only agents: `disallowedTools: [Write, Edit]`.

### 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

## Declaring a Data Store

If your agent produces persistent project-level data (findings, benchmarks, patches), declare a data domain using the `.epost-data/` convention. See the `data-store` skill for the full convention and gitignore rules.

**Template — add to agent system prompt body:**

```markdown
## Data Store
- **DB:** `.epost-data/{domain}/{domain}.json` (if exists)
- **Artifacts:** `.epost-data/{domain}/artifacts/` (if exists)
- **Schema:** `.claude/assets/{domain}-schema.json`
```

**Steps:**
1. Create schema at `packages/{pkg}/assets/{domain}-schema.json`
2. Add the "Data Store" section above to the agent's system prompt
3. Reference paths in commands with `(if exists)` guards
4. Register the domain in `data-store` skill's Domain Registry table

## References

- `references/agent-creation-guide.md` — Full creation workflow, validation rules, testing, organization