Sub Agent Creator

Sub-Agent Creator

This skill provides guidance for creating effective OpenKosmos sub-agents using the AGENT.md file format.

About Sub-Agents

Sub-agents are specialized, task-scoped AI agents that a parent agent can delegate work to via spawn_subagent or spawn_multiple_subagents tools. They run as lightweight, non-streaming conversation loops with their own tool access, system prompt, and optional context inheritance.

Sub-Agent vs Agent

Runtime Limits

Context Access Modes

Sub-agents can access the parent conversation's context at three levels:

• isolated (default): No parent context. Sub-agent works only with its own system prompt and the task description. Best for independent, self-contained tasks.
• parent_summary: Receives a condensed summary of the parent conversation. Good for tasks that need awareness of what the user discussed but don't need full details.
• full_history: Receives the full parent conversation history. Use sparingly — this consumes significant context window and is only needed when the sub-agent must understand the complete discussion.

AGENT.md File Format

Every sub-agent is defined by a single AGENT.md file with YAML front-matter and a Markdown body:

agents/{agent-name}/
└── AGENT.md

Structure

---
# Claude Code standard fields
name: my-agent
description: What this sub-agent does and when to delegate to it.
model: inherit
maxTurns: 25

# OpenKosmos extension fields (under x-openkosmos namespace)
x-openkosmos:
  display_name: My Agent
  emoji: "🤖"
  version: "1.0.0"
  context_access: isolated
  inherit_mcp_servers: true
  inherit_skills: true
  inherit_knowledge_base: true
---

System prompt goes here as Markdown body...

Required Fields

Claude Code Standard Fields (optional)

OpenKosmos Extension Fields (under x-openkosmos)

For the complete field reference with detailed semantics, see references/openkosmos-extensions.md.

Core Principles

System Prompt Writing

The Markdown body of AGENT.md becomes the sub-agent's system prompt. Follow these principles:

1. Be task-oriented: Start with "You are a specialized sub-agent for [specific purpose]." Clearly state what the sub-agent does.
2. Be concise: Sub-agents have limited turns. Every token in the system prompt reduces the working context. Aim for 200–500 words.
3. Define clear completion criteria: State explicitly what "done" looks like so the sub-agent knows when to stop.
4. Include step-by-step instructions: Numbered steps help the sub-agent execute methodically within its turn limit.
5. Specify output format: Define how results should be returned to the parent agent.

Tool Configuration Strategy

• Principle of least privilege: Only grant tools the sub-agent actually needs.
• builtin_tools whitelist: When set (non-empty), the sub-agent can ONLY use listed tools. Prefer this for security-sensitive tasks.
• inherit_mcp_servers: true: Convenient for sub-agents that need the same external services as the parent. Set to false if the sub-agent should be sandboxed.
• Claude Code tools field: Maps to OpenKosmos built-in tools automatically on import (e.g., Read → read_file, Bash → execute_command).

Context Access Selection Guide

Default to isolated unless there's a clear reason for broader access.

Model Selection

• inherit (default): Uses the same model as the parent agent. Recommended for most cases.
• Specific model: Use when the sub-agent needs a different capability level (e.g., a simpler model for repetitive tasks, or a more capable model for complex reasoning).

Sub-Agent Creation Process

Follow these steps to create a new sub-agent:

Step 1: Understand the Sub-Agent's Purpose

Clarify with the user:

• What specific task will this sub-agent handle?
• When should the parent agent delegate to it?
• What tools and resources does it need?
• Does it need parent conversation context?

Step 2: Plan Configuration

Based on the requirements, determine:

• Tools needed: Which built-in tools, MCP servers, and skills
• Context access: isolated, parent_summary, or full_history
• Constraints: maxTurns limit, workspace isolation
• Inheritance: Whether to inherit parent's MCP servers, skills, knowledge base

Step 3: Write the AGENT.md

Use write_file to create agents/{agent-name}/AGENT.md in the current workspace with:

1. YAML front-matter with all configuration fields
2. Markdown body containing the system prompt

Prefer using write_file directly to create the complete AGENT.md file. This is the most reliable approach since it requires no external dependencies.

If the user prefers a scaffold template, the scripts/init_agent.py script can generate a starter AGENT.md:

python scripts/init_agent.py <agent-name> --path <output-directory>

Step 4: Move to Profile Agents Directory

⚠️ IMPORTANT: The AGENT.md file created in Step 3 is in the chat workspace directory, but OpenKosmos reads sub-agents from the profile-level agents directory. You must move the file to the correct location.

Source:      {workspace}/agents/{agent-name}/AGENT.md
Destination: C:/Users/<username>/AppData/Roaming/openkosmos-app/profiles/<user_alias>/agents/{agent-name}/AGENT.md

Steps:

1. Ask the user for their OpenKosmos profile alias (typically in format username_org, e.g. username_org), or help them find it
2. Use execute_command to move the entire agents/{agent-name}/ folder to the profile agents directory

Example:

# Windows
move "{workspace}\agents\{agent-name}" "C:\Users\<username>\AppData\Roaming\openkosmos-app\profiles\<user_alias>\agents\{agent-name}"

# macOS / Linux
mv "{workspace}/agents/{agent-name}" "~/Library/Application Support/openkosmos-app/profiles/<user_alias>/agents/{agent-name}"

Step 5: Sync and Test

After moving the AGENT.md file to the profile agents directory:

1. Tell the user to go to Settings → Sub-Agents and click the Sync button to reload sub-agent configurations
2. The sub-agent should now appear in the Sub-Agents list
3. Assign the sub-agent to a parent agent
4. Test by asking the parent agent to delegate an appropriate task
5. Verify the sub-agent executes correctly and returns useful results

Iterate on the system prompt and configuration based on test results.

Common Design Patterns

For detailed patterns with complete AGENT.md examples, see references/agent-patterns.md:

1. Tool Specialist — Focused on specific tool operations (code review, file processing)
2. Research Assistant — Information retrieval and knowledge synthesis
3. Task Executor — Command execution and automation
4. Collaborative — Context-aware tasks requiring parent conversation awareness

Complete Example

Here is a complete, production-ready AGENT.md for a code reviewer sub-agent:

---
name: code-reviewer
description: Expert code review specialist. Delegate to this sub-agent when you need thorough code review with focus on bugs, security issues, performance, and best practices.
model: inherit
maxTurns: 15

x-openkosmos:
  display_name: Code Reviewer
  emoji: "🔍"
  version: "1.0.0"
  builtin_tools:
    - read_file
    - search_text_in_files
    - search_files
  context_access: parent_summary
  inherit_mcp_servers: false
  inherit_skills: false
  inherit_knowledge_base: true
---

You are a senior code reviewer ensuring high standards of code quality.

When invoked with code to review:
1. Read the specified files using read_file
2. Analyze for: bugs, security vulnerabilities, performance issues, code style
3. Search for related patterns in the codebase using search_text_in_files
4. Return a structured review report

## Review Report Format

Return findings in this structure:

### Critical Issues
- [List any bugs or security vulnerabilities]

### Improvements
- [List performance and maintainability suggestions]

### Positive Observations
- [Note well-written code patterns]

### Summary
[One paragraph overall assessment with priority recommendations]

## Guidelines
- Focus on actionable feedback — every finding should have a suggested fix
- Prioritize: security > correctness > performance > style
- Reference specific line numbers when pointing out issues
- Keep the review concise — aim for quality over quantity

Resources

• scripts/init_agent.py: Generate a starter AGENT.md template with proper structure
• scripts/quick_validate.py: Validate AGENT.md format and required fields
• references/agent-patterns.md: Four common sub-agent design patterns with complete examples
• references/openkosmos-extensions.md: Complete reference for all OpenKosmos x-openkosmos extension fields

Source: microsoft/open-kosmos — distributed by TomeVault.