BMAD-METHOD/docs/explanation/core-concepts/what-are-agents.md

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Agents

Agents are AI assistants that help you accomplish tasks. Each agent has a unique personality, specialized capabilities, and an interactive menu.

Agent Types

BMAD has two primary agent types, designed for different use cases:

Simple Agents

Self-contained, focused, ready to use.

Simple agents are complete in a single file. They excel at well-defined tasks and require minimal setup.

Best for:

• Single-purpose assistants (code review, documentation, commit messages)
• Quick deployment
• Projects that don't require persistent memory
• Getting started fast

Example: A commit message agent that reads your git diff and generates conventional commits.

Expert Agents

Powerful, memory-equipped, domain specialists.

Expert agents have a sidecar - a companion folder containing additional instructions, workflows, and memory files. They remember context across sessions and handle complex, multi-step tasks.

Best for:

• Domain specialists (security architect, game designer, product manager)
• Tasks requiring persistent memory
• Complex workflows with multiple stages
• Projects that grow over time

Example: A game architect that remembers your design decisions, maintains consistency across sprints, and coordinates with other specialists.

Key Differences

Feature	Simple	Expert
Files	Single file	Agent + sidecar folder
Memory	Session only	Persistent across sessions
Capabilities	Focused scope	Multi-domain, extensible
Setup	Zero config	Sidecar initialization
Best Use	Specific tasks	Ongoing projects

Agent Components

All agents share these building blocks:

Persona

• Role - What the agent does (expertise domain)
• Identity - Who the agent is (personality, character)
• Communication Style - How the agent speaks (tone, voice)
• Principles - Why the agent acts (values, decision framework)

Capabilities

• Skills, tools, and knowledge the agent can apply
• Mapped to specific menu commands

Menu

• Interactive command list
• Triggers, descriptions, and handlers
• Auto-includes help and exit options

Critical Actions (optional)

• Instructions that execute before the agent starts
• Enable autonomous behaviors (e.g., "check git status before changes")

Which Should You Use?

Choose Simple when:

• You need a task done quickly and reliably
• The scope is well-defined and won't change much
• You don't need the agent to remember things between sessions

Choose Expert when:

• You're building something complex over time
• The agent needs to maintain context (project history, decisions)
• You want the agent to coordinate workflows or other agents
• Domain expertise requires specialized knowledge bases

Creating Custom Agents

BMAD provides the BMAD Builder (BMB) module for creating your own agents. See the Agent Creation Guide for step-by-step instructions.

Customizing Existing Agents

You can modify any agent's behavior without editing core files. See BMAD Customization for details. It is critical to never modify an installed agents .md file directly and follow the customization process, this way future updates to the agent or module its part of will continue to be updated and recompiled with the installer tool, and your customizations will still be retained.

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Next: Learn about Workflows to see how agents accomplish complex tasks.