Subagents Guide

Subagents Guide

What Are Subagents?

Subagents are pre-configured AI personalities that Claude Code delegates to handle specific task types. Each operates independently with:

• Separate context — Prevents main conversation pollution, keeps focus on high-level objectives
• Custom system prompt — Guides behavior for specific domains
• Dedicated tools — Granular permission control per subagent
• Reusability — Available across projects, shareable with teams

Key Benefits

When to Use Subagents

Delegate when:

• Task matches a pre-defined expertise area
• You want isolated context for deep work
• Multiple independent tasks can run in parallel
• Tool access should be restricted
• You need consistent behavior across projects

Don't delegate:

• Simple one-off changes (≤3 files)
• Active debugging with rapid iteration
• Tasks requiring main conversation context

Quick Start

# Open subagents interface (Recommended approach)
/agents

# Or create manually: project subagents go here
mkdir -p .claude/agents

# User subagents (available everywhere)
mkdir -p ~/.claude/agents

Steps:

1. Run /agents command
2. Select "Create New Agent"
3. Describe purpose, select tools, customize system prompt
4. Save — subagent is now available

File Format

Subagents are Markdown files with YAML frontmatter:

---
name: subagent-name
description: When this subagent should be used and its expertise area
tools: Read, Write, Bash  # Optional — inherit all if omitted
model: sonnet            # Optional — sonnet, opus, haiku, or 'inherit'
---

Your system prompt goes here. Define role, capabilities, constraints,
and specific instructions. Include examples, checklists, and best practices.

Configuration Fields

File Locations & Priority

Project subagents override user-level ones with the same name.

Tool Configuration Best Practices

Principle: Least Privilege

Only grant tools necessary for the subagent's purpose. This:

• Improves security and focus
• Prevents unintended actions
• Makes subagent behavior more predictable

Common tool combinations:

# Code reviewer
tools: Read, Grep, Glob, Bash

# Data analyst
tools: Read, Write, Bash

# Test automation
tools: Bash, Read, Edit, Write

# Debugger
tools: Read, Edit, Bash, Grep, Glob

# Documentation writer
tools: Read, Write, Glob, Grep

Omit tools to let subagent inherit all (including MCP tools).

Invocation Methods

Automatic Delegation

Claude Code proactively delegates when:

• Task description matches subagent purpose
• Subagent description field matches context
• Appropriate tools are configured

To encourage automatic use, include "proactively" in description:

description: Use proactively to run tests and fix failures

Explicit Invocation

Request a subagent directly:

Use the code-reviewer subagent to check my recent changes
Have the debugger investigate this test failure
Ask the data-scientist subagent for a SQL analysis

Example Subagents

Code Reviewer

---
name: code-reviewer
description: Expert code review specialist. Use proactively after writing code.
tools: Read, Grep, Glob, Bash
model: inherit
---

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

When invoked, run git diff to identify recent changes and review modified files.

Review checklist:
- Readability and naming
- No duplicated code
- Proper error handling
- No exposed secrets
- Input validation implemented
- Test coverage adequate
- Performance considerations addressed

Organize feedback by priority:
- Critical issues (must fix)
- Warnings (should fix)
- Suggestions (consider improving)

Include specific examples for all recommendations.

Test Automation

---
name: test-runner
description: Test automation expert. Use proactively to run tests and fix failures.
tools: Bash, Read, Edit
---

You are a test automation specialist. When you see code changes, proactively run appropriate tests.

If tests fail:
1. Analyze failure messages and logs
2. Identify root cause
3. Fix the issue while preserving test intent
4. Re-run tests to confirm

For each failure, provide:
- Root cause explanation
- Code fix
- Prevention recommendations

Focus on fixing the underlying issue, not just symptoms.

Debugger

---
name: debugger
description: Debugging specialist. Use proactively when encountering errors or unexpected behavior.
tools: Read, Edit, Bash, Grep, Glob
---

You are an expert debugger specializing in root cause analysis.

Debugging process:
1. Capture error message and stack trace
2. Identify reproduction steps
3. Isolate the failure location
4. Implement minimal fix
5. Verify solution works

For each issue, provide:
- Root cause explanation with evidence
- Specific code fix
- Testing approach
- Prevention recommendations

Focus on fixing the underlying issue, not just symptoms.

Best Practices

Design focused subagents

• Single, clear responsibility per subagent
• Improves performance and predictability
• Easier to test and iterate

Write detailed system prompts

• Include specific instructions and examples
• Define constraints and decision rules
• More guidance = better performance

Limit tool access intentionally

• Only grant necessary tools
• Improves security and focus
• Prevents unintended side effects

Start with Claude-generated agents

• Generate initial subagent with Claude, then customize
• Provides solid foundation for iteration
• Better results than building from scratch

Version control project subagents

• Check .claude/agents/ into git
• Team benefits from shared, improved subagents
• Track subagent evolution over time

Use specific descriptions for auto-delegation

• Include action verbs: "use proactively", "automatically", "must be used"
• Match task keywords from your workflow
• Example: "Use proactively to analyze errors and fix bugs"

Advanced: Chaining Subagents

For complex workflows, sequence multiple subagents:

> First use the code-analyzer subagent to find performance issues,
  then use the optimizer subagent to fix them

Each subagent completes its work, then the next is invoked with its results.

Performance Considerations

Latency trade-off:

• Subagents preserve main context (allows longer sessions)
• Each subagent invocation requires initial context gathering
• Suitable for focused, substantial work (not quick tweaks)

When to use subagents: Substantial work, deep investigation, complex logic, long tasks When to skip: Quick edits (≤3 files), rapid iteration, simple clarifications

Management

Using /agents Command (Recommended)

/agents

Provides interactive interface to:

• View all available subagents
• Create new subagents with guided setup
• Edit existing subagents and tool permissions
• Delete custom subagents
• See active subagents when duplicates exist

Direct File Management

Create project subagent:

mkdir -p .claude/agents
cat > .claude/agents/test-runner.md << 'EOF'
---
name: test-runner
description: Use proactively to run tests and fix failures
---

[Your system prompt here]
EOF

Create user subagent:

mkdir -p ~/.claude/agents
# Create file same way as project subagent

Related Documentation

• Slash commands
• Settings — Configure subagent models and defaults
• Hooks — Automate workflows with event handlers