Agent Creation

Design, create, and maintain custom GitHub Copilot agents for VS Code that enhance developer productivity through specialized AI personas.

When to Use This Skill

• Creating a new custom agent for a specific development role
• Updating an existing agent to improve its effectiveness
• Designing agent workflows with handoffs between agents
• Selecting the right tools for an agent's capabilities

Agent File Structure

Agents live in .github/agents/ as .agent.md files:

---
name: {Agent Name}
description: {One-line description for chat input placeholder}
model: Claude Opus 4.6
tools:
  - {tool1}
  - {tool2}
handoffs:  # Optional
  - label: {Button Text}
    agent: {target-agent}
    prompt: {Prompt to send}
    send: false
---

# {Agent Name}

{Role description and core purpose}

## Core Principles
{Key principles the agent follows}

## Workflow
{How the agent approaches tasks}

## Patterns & Examples
{Code patterns, templates, examples}

Tool Selection Guide

Agent Type	Recommended Tools
Code Developer	codebase, editFiles, createFile, readFile, runInTerminal, problems, usages
Code Reviewer	codebase, readFile, problems, usages, changes
Planner	codebase, readFile, search, fetch
Documentation	codebase, readFile, createFile, editFiles, fetch
Testing	codebase, editFiles, runInTerminal, testFailure, problems

Available Tools Reference

Core: codebase, editFiles, createFile, readFile, runInTerminal, search Context: problems, usages, testFailure, changes External: fetch, githubRepo

Design Principles

1. Role-Focused — One agent per role/responsibility with clear boundaries
2. Tool-Appropriate — Select only the tools the agent needs
3. Quality Instructions — Be specific and actionable, include code examples
4. Handoff-Aware — Design handoffs for natural task transitions

Agent Templates

Developer Agent

---
name: {Language} Expert
description: Expert {language} developer specializing in {specialty}
model: Claude Opus 4.6
tools:
  - codebase
  - editFiles
  - createFile
  - readFile
  - runInTerminal
  - problems
  - usages
  - testFailure
---

# {Language} Expert

You are a senior {language} developer...

## Core Principles
...

## Development Workflow
...

## Code Patterns
...

Reviewer Agent

---
name: Code Reviewer
description: Reviews code for quality, security, and best practices
model: Claude Opus 4.6
tools:
  - codebase
  - readFile
  - problems
  - usages
  - changes
---

Planner Agent

---
name: Planner
description: Creates implementation plans without making code changes
model: Claude Opus 4.6
tools:
  - codebase
  - readFile
  - search
  - fetch
handoffs:
  - label: Start Implementation
    agent: {implementation-agent}
    prompt: Implement the plan above.
    send: false
---

Workflow

1. Understand Requirements — What role, tasks, tools, and handoffs?
2. Research — Check existing agents in .github/agents/ for patterns
3. Design — Structure with frontmatter, principles, workflow, and examples
4. Create — Write to .github/agents/{agent-name}.agent.md (kebab-case)
5. Validate — Test the agent with realistic prompts

Guidelines

• Use kebab-case for agent filenames
• Keep descriptions concise but descriptive
• Include concrete code examples in agent instructions
• Design handoffs for natural task transitions between agents
• Consider whether a skill might be more appropriate than an agent