Claude Code Agents

Guide for creating custom agents that provide specialized behaviors and tool access for specific tasks.

When to Use This Skill

Activate this skill when:

• Creating custom agent types for specific workflows
• Defining agent behaviors and tool permissions
• Configuring agent capabilities
• Understanding agent vs skill differences
• Implementing domain-specific agents

What Are Agents?

Agents are specialized Claude instances with:

• Specific tool access: Limited or specialized tool sets
• Defined behaviors: Pre-configured instructions and constraints
• Task focus: Optimized for particular workflows
• Autonomous operation: Can execute multi-step tasks independently

Agents vs Skills

| Feature | Agents | Skills | |---------|--------|--------| | Activation | Explicitly launched via Task tool | Auto-activated based on context | | Tool Access | Configurable, can be restricted | Inherit from parent context | | State | Independent, isolated | Share parent context | | Use Case | Complex multi-step tasks | Knowledge and guidelines | | Persistence | Single execution | Always available when loaded |

Agent File Structure

Location

Agents are defined in markdown files located in:

• Plugin: <plugin-root>/agents/
• User-level: .claude/agents/

File Naming

• Use kebab-case: code-reviewer.md
• File name becomes the agent type
• Be descriptive about the agent's purpose

Basic Agent Format

markdown
---
name: code-reviewer
description: Reviews code for quality and best practices
tools: Read, Grep, Glob
model: sonnet
---

You are a code reviewer. Analyze code for quality, security, and best practices.

## Workflow

1. **Find files**: Glob to locate target files
2. **Read code**: Examine contents
3. **Check patterns**: Grep for anti-patterns
4. **Report**: Provide prioritized feedback

## Guidelines

- **Specific**: Reference file:line locations
- **Actionable**: Suggest concrete fixes
- **Prioritized**: Critical issues first

Agent Writing Style

Effective agents use direct, imperative language:

Opening Statement

• Do: "You are a role]. Your role is to primary function]."
• Don't: "I am a specialized role] focused on..."

Workflow Steps

• Do: Numbered steps with specific commands
• Don't: Bullet lists describing capabilities

Guidelines Section

• Do: Single-word bold labels with brief explanations
• Don't: Verbose explanations of best practices

Agent Configuration

YAML Frontmatter

Required and optional fields:

markdown
---
name: agent-name                    # Required: kebab-case identifier
description: Brief description      # Required: What this agent does
tools:                             # Optional: Tool allowlist
  - Read
  - Write
  - Bash
model: sonnet                      # Optional: Model to use (sonnet, opus, haiku)
max_iterations: 10                 # Optional: Maximum task iterations
timeout: 300                       # Optional: Timeout in seconds
---

Tool Allowlist

Restrict agent to specific tools:

• Can read files
• Can search code
• Can find files
• Cannot use Write, Edit, Bash, etc.

Example:

markdown
---
tools: Read, Grep, Glob     
---

No tool restrictions (access to all tools):

markdown
---
# Omit tools field entirely
---

Model Selection

Choose appropriate model for the task:

markdown
---
model: haiku        # Fast, cost-effective for simple tasks
# model: sonnet     # Balanced (default)
# model: opus       # Most capable for complex tasks
---

Common Agent Patterns

Read-Only Analysis Agent

For security scans, code reviews, or audits. Restricted to Read, Grep, Glob.

See: templates/read-only-analyzer.md

Write-Capable Agent

For generating tests, documentation, or code. Includes Write tool.

See: templates/write-capable-agent.md

Full-Access Agent

For refactoring, migrations, or complex modifications. Omit tools field entirely for no restrictions.

See: templates/full-access-agent.md

MCP-Enabled Agent

For browser automation, external APIs, or specialized MCP server tools. Mix core tools with MCP tools.

See: templates/mcp-agent.md

Agent Plugin Configuration

In plugin.json

json
{
  "agents": [
    "./agents/code-reviewer.md",
    "./agents/test-generator.md",
    "./agents/security-analyzer.md"
  ]
}

Directory-Based Loading

json
{
  "agents": "./agents"
}

Loads all .md files in agents/ directory.

Invoking Agents

Agents are launched via the Task tool:

python
# In parent Claude conversation
Task(
    subagent_type="code-reviewer",
    description="Review authentication module",
    prompt="""
    Review the authentication module for:
    - Security vulnerabilities
    - Error handling
    - Input validation
    - Best practices
    """
)

Agent Communication

Input to Agent

• Task description
• Detailed prompt
• Access to conversation history (if configured)

Output from Agent

• Final report/result
• No ongoing dialogue
• One-time execution

Best Practices

Clear Purpose

Each agent should have a specific, well-defined purpose:

markdown
---
name: migration-helper
description: Assists with database schema migrations
---

# Database Migration Agent

Specialized in creating and validating database migrations.

Appropriate Tool Access

Only grant necessary tools:

markdown
---
# Analysis agent - read-only
tools: Read, Grep, Glob
---

markdown
---
# Implementation agent - can modify
tools: Read, Write, Edit, Glob, Grep
---

Model Selection

Match model to task complexity:

• haiku: Simple, repetitive tasks
• sonnet: Standard tasks (default)
• opus: Complex reasoning required

Iteration Limits

Set appropriate limits for task complexity:

markdown
---
max_iterations: 5   # Simple, focused task
# max_iterations: 20  # Complex, multi-step workflow
---

Clear Instructions

Provide explicit behavior guidelines:

markdown
# Testing Agent

## Mandatory Requirements

- Generate tests for ALL public methods
- Achieve minimum 80% code coverage
- Include edge cases and error scenarios
- Use project's testing framework conventions

## Constraints

- Do not modify source code
- Follow existing test file naming patterns
- Use appropriate assertions

Security Considerations

Tool Restrictions

Limit dangerous operations:

markdown
---
# Don't give Bash access to untrusted agents
tools:
  - Read
  - Write  # Safer than arbitrary shell commands
---

Input Validation

Validate agent inputs:

markdown
# Deployment Agent

Before deploying:
1. Verify target environment is valid
2. Check deployment permissions
3. Validate configuration
4. Confirm destructive operations

Sensitive Data

Never hardcode:

• Credentials
• API keys
• Private URLs
• Access tokens

Agent Examples

For complete, production-ready agent templates:

• templates/basic-agent.md - Official minimal example
• templates/read-only-analyzer.md - Security analyzer pattern
• templates/write-capable-agent.md - Test generator pattern
• templates/full-access-agent.md - Refactoring pattern (no tool restrictions)
• templates/mcp-agent.md - Browser testing with MCP tools

Troubleshooting

Agent Not Found

• Verify agent file location matches plugin.json
• Check file naming (kebab-case, .md extension)
• Ensure plugin is properly installed

Tool Access Denied

• Check tools allowlist in frontmatter
• Verify tool names match exactly
• Ensure parent context permits delegation

Unexpected Behavior

• Review agent instructions for clarity
• Check model selection appropriateness
• Verify iteration limits aren't too restrictive
• Test with verbose output

References

Templates directory:

• templates/basic-agent.md - Official minimal example
• templates/read-only-analyzer.md - Security analysis pattern
• templates/write-capable-agent.md - Test generation pattern
• templates/full-access-agent.md - Refactoring pattern (no tool restrictions)
• templates/mcp-agent.md - MCP tools pattern (browser automation)

Documentation:

• Claude Code Agents: https://code.claude.com/docs/en/agents
• Task Tool: https://code.claude.com/docs/en/tools/task