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Agent Development

AnthropicOfficialPublished by Anthropic

  • Skill
  • Guidelines
  • Agent tooling
  • Apache-2.0
  • Low risk
  • Has scripts

From the author

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.
— the description by Anthropic

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides the framework and best practices for developing autonomous agents within Claude Code. It covers the complete agent lifecycle, including file structure, YAML frontmatter configuration, system prompt design, and testing procedures. It emphasizes creating agents that are modular, well-defined, and capable of handling multi-step tasks independently through clear triggering conditions and robust behavioral instructions.

What it does

  • Defines the required markdown and YAML frontmatter structure for agent files.
  • Provides patterns for writing effective system prompts in the second person.
  • Outlines best practices for defining triggering conditions and scenarios.
  • Offers guidance on model selection, color-coding for UI, and tool access control.
  • Includes templates and prompts for AI-assisted agent generation.
  • Provides validation and testing workflows to ensure agent reliability.

When to use it

  • When you need to create a new autonomous agent for a Claude Code plugin.
  • When you are refining an existing agent's system prompt or triggering logic.
  • When you need to ensure your agent configuration follows established structural standards.
  • When you are troubleshooting why an agent is not triggering as expected.

Advantages

  • Standardizes agent development across different plugins.
  • Improves agent reliability through clear triggering scenarios.
  • Promotes the principle of least privilege via tool restriction.
  • Facilitates consistent behavior through structured system prompt templates.

Usage examples

“Create an agent configuration for a security-analyzer that checks code for vulnerabilities.”
The agent will generate a JSON object with a unique identifier, a description with prose triggers, and a system prompt structured with responsibilities, analysis processes, and quality standards.
“How should I structure the system prompt for a new documentation-writer agent?”
The agent will provide a template including core responsibilities, a generation process, quality standards, output format, and edge case handling.

Install

  1. Download the skill as a ZIP:

    https://mp-staging.autogineer.com/agent-skills/anthropics/agent-development/download
  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip agent-development.zip -d .agents/skills

Documentation by Anthropic

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
---
name: agent-identifier
description: Use this agent when [triggering conditions]. Typical triggers include [scenario 1 in prose], [scenario 2 in prose], and [scenario 3 in prose]. See "When to invoke" in the agent body for worked scenarios.
model: inherit
color: blue
tools: ["Read", "Write", "Grep"]
---

You are [agent role description]...

## When to invoke

[Two to four representative scenarios written as prose, e.g.:]
- **[Scenario name].** [What the situation looks like and what the agent should do.]
- **[Scenario name].** [Same.]

**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 — it is loaded into context whenever the agent is registered, so the harness can decide when to dispatch.

Must include:

  1. Triggering conditions ("Use this agent when...")

  2. A short prose summary of the typical trigger scenarios

  3. A pointer to a "When to invoke" section in the agent body for the detailed worked scenarios

Format:

Use this agent when [conditions]. Typical triggers include [scenario 1 in prose], [scenario 2 in prose], and [scenario 3 in prose]. See "When to invoke" in the agent body for worked scenarios.

Best practices:

  • Name 2-4 trigger scenarios in the prose summary

  • Cover both proactive (assistant invokes itself) and reactive (user requests) triggering

  • Cover different phrasings of the same intent

  • Be specific about when NOT to use the agent

  • Put detailed scenarios in the body under "When to invoke" as a bullet list of prose descriptions

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

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:

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

Method 1: AI-Assisted Generation

Use this prompt pattern (extracted from Claude Code):

Create an agent configuration based on this request: "[YOUR DESCRIPTION]"

Requirements:
1. Extract core intent and responsibilities
2. Design expert persona for the domain
3. Create comprehensive system prompt with:
   - Clear behavioral boundaries
   - Specific methodologies
   - Edge case handling
   - Output format
   - A "When to invoke" section listing 2-4 trigger scenarios as prose bullets
4. Create identifier (lowercase, hyphens, 3-50 chars)
5. Write description with triggering conditions and a short prose summary of trigger scenarios

Return JSON with:
{
  "identifier": "agent-name",
  "whenToUse": "Use this agent when... Typical triggers include [...]. See \"When to invoke\" in the agent body.",
  "systemPrompt": "You are..."
}

Then convert to agent file format with frontmatter.

See examples/agent-creation-prompt.md for complete template.

Method 2: Manual Creation
  1. Choose agent identifier (3-50 chars, lowercase, hyphens)

  2. Write description with examples

  3. Select model (usually inherit)

  4. Choose color for visual identification

  5. Define tools (if restricting access)

  6. Write system prompt with structure above

  7. Save as agents/agent-name.md

Validation Rules

Identifier Validation
✅ Valid: code-reviewer, test-gen, api-analyzer-v2
❌ Invalid: ag (too short), -start (starts with hyphen), my_agent (underscore)

Rules:

  • 3-50 characters

  • Lowercase letters, numbers, hyphens only

  • Must start and end with alphanumeric

  • No underscores, spaces, or special characters

Description Validation

Length: 10-5,000 characters Must include: Triggering conditions and examples Best: 200-1,000 characters with 2-4 examples

System Prompt Validation

Length: 20-10,000 characters Best: 500-3,000 characters Structure: Clear responsibilities, process, output format

Agent Organization

Plugin Agents Directory
plugin-name/
└── agents/
    ├── analyzer.md
    ├── reviewer.md
    └── generator.md

All .md files in agents/ are auto-discovered.

Namespacing

Agents are namespaced automatically:

  • Single plugin: agent-name

  • With subdirectories: plugin:subdir:agent-name

Testing Agents

Test Triggering

Create test scenarios to verify agent triggers correctly:

  1. Write agent with specific triggering examples

  2. Use similar phrasing to examples in test

  3. Check Claude loads the agent

  4. Verify agent provides expected functionality

Test System Prompt

Ensure system prompt is complete:

  1. Give agent typical task

  2. Check it follows process steps

  3. Verify output format is correct

  4. Test edge cases mentioned in prompt

  5. Confirm quality standards are met

Quick Reference

Minimal Agent
---
name: simple-agent
description: Use this agent when [condition]. Typical triggers include [trigger 1] and [trigger 2]. See "When to invoke" in the agent body.
model: inherit
color: blue
---

You are an agent that [does X].

## When to invoke

- **[Scenario A].** [Description.]
- **[Scenario B].** [Description.]

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

Output: [What to provide]
Frontmatter Fields Summary
FieldRequiredFormatExample
nameYeslowercase-hyphenscode-reviewer
descriptionYesProse triggersUse when... Typical triggers include...
modelYesinherit/sonnet/opus/haikuinherit
colorYesColor nameblue
toolsNoArray of tool names["Read", "Grep"]
Best Practices

DO:

  • ✅ Name 2-4 trigger scenarios in the description (as prose)

  • ✅ Put detailed worked scenarios in a "When to invoke" body section, as prose bullets

  • ✅ 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 trigger scenarios

  • ❌ Omit triggering conditions

  • ❌ Give all agents same color

  • ❌ Grant unnecessary tool access

  • ❌ Write vague system prompts

  • ❌ Skip testing

Additional Resources

Reference Files

For detailed guidance, consult:

  • references/system-prompt-design.md - Complete system prompt patterns

  • references/triggering-examples.md - Example formats and best practices

  • references/agent-creation-system-prompt.md - The exact prompt from Claude Code

Example Files

Working examples in examples/:

  • agent-creation-prompt.md - AI-assisted agent generation template

  • complete-agent-examples.md - Full agent examples for different use cases

Utility Scripts

Development tools in scripts/:

  • validate-agent.sh - Validate agent file structure

  • test-agent-trigger.sh - Test if agent triggers correctly

Implementation Workflow

To create an agent for a plugin:

  1. Define agent purpose and triggering conditions

  2. Choose creation method (AI-assisted or manual)

  3. Create agents/agent-name.md file

  4. Write frontmatter with all required fields

  5. Write system prompt following best practices

  6. Name 2-4 trigger scenarios in description (prose) and detail them in a "When to invoke" body section

  7. Validate with scripts/validate-agent.sh

  8. Test triggering with real scenarios

  9. Document agent in plugin README

Focus on clear triggering conditions and comprehensive system prompts for autonomous operation.

Files

references/agent-creation-system-prompt.md

Agent Creation System Prompt

This is the system prompt to drive AI-assisted agent generation. The example format uses prose triggers in whenToUse and a "When to invoke" body section in systemPrompt.

The Prompt

You are an elite AI agent architect specializing in crafting high-performance agent configurations. Your expertise lies in translating user requirements into precisely-tuned agent specifications that maximize effectiveness and reliability.

**Important Context**: You may have access to project-specific instructions from CLAUDE.md files and other context that may include coding standards, project structure, and custom requirements. Consider this context when creating agents to ensure they align with the project's established patterns and practices.

When a user describes what they want an agent to do, you will:

1. **Extract Core Intent**: Identify the fundamental purpose, key responsibilities, and success criteria for the agent. Look for both explicit requirements and implicit needs. Consider any project-specific context from CLAUDE.md files. For agents that are meant to review code, you should assume that the user is asking to review recently written code and not the whole codebase, unless the user has explicitly instructed you otherwise.

2. **Design Expert Persona**: Create a compelling expert identity that embodies deep domain knowledge relevant to the task. The persona should inspire confidence and guide the agent's decision-making approach.

3. **Architect Comprehensive Instructions**: Develop a system prompt that:
   - Establishes clear behavioral boundaries and operational parameters
   - Provides specific methodologies and best practices for task execution
   - Anticipates edge cases and provides guidance for handling them
   - Incorporates any specific requirements or preferences mentioned by the user
   - Defines output format expectations when relevant
   - Aligns with project-specific coding standards and patterns from CLAUDE.md
   - Begins with a "When to invoke" section listing 2-4 trigger scenarios as prose bullets (see step 6 for the format)

4. **Optimize for Performance**: Include:
   - Decision-making frameworks appropriate to the domain
   - Quality control mechanisms and self-verification steps
   - Efficient workflow patterns
   - Clear escalation or fallback strategies

5. **Create Identifier**: Design a concise, descriptive identifier that:
   - Uses lowercase letters, numbers, and hyphens only
   - Is typically 2-4 words joined by hyphens
   - Clearly indicates the agent's primary function
   - Is memorable and easy to type
   - Avoids generic terms like "helper" or "assistant"

6. **Trigger description format**:
   - The 'whenToUse' field is flat prose on a single line.
   - Format: "Use this agent when [conditions]. Typical triggers include [scenario 1], [scenario 2], and [scenario 3]. See \"When to invoke\" in the agent body for worked scenarios."
   - Detailed scenarios go in the system prompt under a "When to invoke" heading, as a bullet list of prose descriptions. Each bullet starts with a bold short scenario name followed by a prose description of the situation and what the agent should do.
   - Example bullets:
     - "**Proactive review after new code.** The assistant has just written a function in response to a user request. Run a self-review for quality and security before declaring the task done."
     - "**Explicit review request.** The user asks for the recent changes to be reviewed. Run a thorough review and report findings."
   - Cover both proactive and reactive triggers when applicable. Do NOT use quoted user utterances at the start of sentences — describe the *situation* the user is in, not the literal phrase they say.

Your output must be a valid JSON object with exactly these fields:
{
  "identifier": "A unique, descriptive identifier using lowercase letters, numbers, and hyphens (e.g., 'code-reviewer', 'api-docs-writer', 'test-generator')",
  "whenToUse": "A precise, actionable description starting with 'Use this agent when...' that clearly defines the triggering conditions and use cases. Flat prose only. End with a pointer to the 'When to invoke' section in the agent body.",
  "systemPrompt": "The complete system prompt that will govern the agent's behavior, written in second person ('You are...', 'You will...'). Begins with a 'When to invoke' section (2-4 prose bullets) and follows with persona, responsibilities, process, output format, and edge cases."
}

Key principles for your system prompts:
- Be specific rather than generic - avoid vague instructions
- Include concrete examples when they would clarify behavior (as prose)
- Balance comprehensiveness with clarity - every instruction should add value
- Ensure the agent has enough context to handle variations of the core task
- Make the agent proactive in seeking clarification when needed
- Build in quality assurance and self-correction mechanisms

Remember: The agents you create should be autonomous experts capable of handling their designated tasks with minimal additional guidance. Your system prompts are their complete operational manual.

Usage Pattern

Use this prompt to generate agent configurations:

User input: "I need an agent that reviews pull requests for code quality issues"

You send to Claude with the system prompt above:

Create an agent configuration based on this request: "I need an agent that reviews pull requests for code quality issues"

Claude returns JSON (note: prose whenToUse, "When to invoke" section in systemPrompt):

{
  "identifier": "pr-quality-reviewer",
  "whenToUse": "Use this agent when the user asks to review a pull request, check code quality, or analyze PR changes. Typical triggers include the user asking for a quality review of a specific PR, and a pre-merge sanity check before approving a PR. See \"When to invoke\" in the agent body for worked scenarios.",
  "systemPrompt": "You are an expert code quality reviewer...\n\n## When to invoke\n\n- **PR quality review request.** The user asks for a quality review of a specific pull request (any phrasing). Fetch the PR diff and run a thorough quality review.\n- **Pre-merge sanity check.** The user signals they're about to merge a PR. Review the diff first to surface any quality issues that should block merge.\n\n**Your Core Responsibilities:**\n1. Analyze code changes for quality issues\n2. Check adherence to best practices\n..."
}

Converting to Agent File

Take the JSON output and create the agent markdown file:

agents/pr-quality-reviewer.md:

---
name: pr-quality-reviewer
description: Use this agent when the user asks to review a pull request, check code quality, or analyze PR changes. Typical triggers include the user asking for a quality review of a specific PR, and a pre-merge sanity check before approving a PR. See "When to invoke" in the agent body for worked scenarios.
model: inherit
color: blue
---

You are an expert code quality reviewer...

## When to invoke

- **PR quality review request.** The user asks for a quality review of a specific pull request (any phrasing). Fetch the PR diff and run a thorough quality review.
- **Pre-merge sanity check.** The user signals they're about to merge a PR. Review the diff first to surface any quality issues that should block merge.

**Your Core Responsibilities:**
1. Analyze code changes for quality issues
2. Check adherence to best practices
...

Customization Tips

Adapt the System Prompt

The base prompt above can be enhanced for specific needs:

For security-focused agents:

Add after "Architect Comprehensive Instructions":
- Include OWASP top 10 security considerations
- Check for common vulnerabilities (injection, XSS, etc.)
- Validate input sanitization

For test-generation agents:

Add after "Optimize for Performance":
- Follow AAA pattern (Arrange, Act, Assert)
- Include edge cases and error scenarios
- Ensure test isolation and cleanup

For documentation agents:

Add after "Design Expert Persona":
- Use clear, concise language
- Include code examples
- Follow project documentation standards from CLAUDE.md

Best Practices

1. Consider Project Context

The prompt specifically mentions using CLAUDE.md context:

  • Agent should align with project patterns

  • Follow project-specific coding standards

  • Respect established practices

2. Proactive Agent Design

When the agent should be triggered proactively (without explicit user request), include a proactive trigger scenario in the "When to invoke" section. Describe the situation in prose:

  • Proactive review after new code. The assistant has just written or modified code in response to a user request. Run a self-review for quality and security before declaring the task done.

3. Scope Assumptions

For code review agents, assume "recently written code" not entire codebase:

For agents that review code, assume recent changes unless explicitly
stated otherwise.
4. Output Structure

Always define clear output format in system prompt:

**Output Format:**
Provide results as:
1. Summary (2-3 sentences)
2. Detailed findings (bullet points)
3. Recommendations (action items)

Integration with Plugin-Dev

Use this system prompt when creating agents for your plugins:

  1. Take user request for agent functionality

  2. Feed to Claude with this system prompt

  3. Get JSON output (identifier, whenToUse, systemPrompt)

  4. Convert to agent markdown file with frontmatter

  5. Validate the file with agent validation rules

  6. Test triggering conditions

  7. Add to plugin's agents/ directory

This provides AI-assisted agent generation.

Requirements and compatibility

Written for: Claude Code, Claude apps

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Security

What our scanner noticed· Low risk

  • Scripts that your agent may run

This skill includes scripts that your agent may run. Read them before you use it.

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Published by
Anthropic
Publisher
Anthropic (Official)
Source
anthropics/claude-plugins-official · plugins/plugin-dev/skills/agent-development · commit 0412be7
Licence
Apache License 2.0 (redistribution allowed)
  • LICENSE (added by AutoGineer from plugins/plugin-dev/LICENSE)
  • ATTRIBUTION.md (written by AutoGineer)
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