Subagent Creator

Sub-agent Creator

Create specialized AI sub-agents for Codex that handle specific tasks with customized prompts and tool access.

Sub-agent File Format

Sub-agents are Markdown files with YAML frontmatter stored in:

• Project: .codex/agents/ (higher priority)
• User: ~/.codex/agents/ (lower priority)

Structure

---
name: subagent-name
description: When to use this subagent (include "use proactively" for auto-delegation)
tools: Tool1, Tool2, Tool3  # Optional - inherits all if omitted
model: sonnet               # Optional - sonnet/opus/haiku/inherit
permissionMode: default     # Optional - default/acceptEdits/bypassPermissions/plan
skills: skill1, skill2      # Optional - auto-load skills
---

System prompt goes here. Define role, responsibilities, and behavior.

Configuration Fields

Creation Workflow

1. Gather requirements: Ask about the sub-agent's purpose, when to use it, and required capabilities
2. Choose scope: Project (.codex/agents/) or user (~/.codex/agents/)
3. Define configuration: Name, description, tools, model
4. Write system prompt: Clear role, responsibilities, and output format
5. Create file: Write the .md file to the appropriate location

Writing Effective Sub-agents

Description Best Practices

The description field is critical for automatic delegation:

# Good - specific triggers
description: Expert code reviewer. Use PROACTIVELY after writing or modifying code.

# Good - clear use cases
description: Debugging specialist for errors, test failures, and unexpected behavior.

# Bad - too vague
description: Helps with code

System Prompt Guidelines

1. Define role clearly: "You are a [specific expert role]"
2. List actions on invocation: What to do first
3. Specify responsibilities: What the sub-agent handles
4. Include guidelines: Constraints and best practices
5. Define output format: How to structure responses

Tool Selection

• Read-only tasks: Read, Grep, Glob, Bash
• Code modification: Read, Write, Edit, Grep, Glob, Bash
• Full access: Omit tools field

See references/available-tools.md for complete tool list.

Example Sub-agents

See references/examples.md for complete examples:

• Code Reviewer
• Debugger
• Data Scientist
• Test Runner
• Documentation Writer
• Security Auditor

Template

Copy from assets/subagent-template.md to start a new sub-agent.

Quick Start Example

Create a code reviewer sub-agent:

mkdir -p .codex/agents

Write to .codex/agents/code-reviewer.md:

---
name: code-reviewer
description: Reviews code for quality and security. Use proactively after code changes.
tools: Read, Grep, Glob, Bash
model: inherit
---

You are a senior code reviewer.

When invoked:
1. Run git diff to see changes
2. Review modified files
3. Report issues by priority

Focus on:
- Code readability
- Security vulnerabilities
- Error handling
- Best practices

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