(Custom) Agent

Components

(Custom) Agent

Sessions handling review, investigation, build, or other varied tasks all within the same conversation can quickly flood the main context.

That’s when custom agents (or subagents) come into play: each dedicated to one task type, with its own model, tool access and system prompt.

They allow delegating tasks or running parallel work during a session without flooding the main context, or without having to initiate a new session with a pre-configured agent.

Format: Claude Code

repository/
└── .claude/
    └── agents/
        └── agent-name.md
~/.claude/
└── agents/
    └── agent-name.md
~/.claude/plugins/cache/<marketplace>/<plugin>/
└── agents/
    └── agent-name.md

---
name: agent-name
description: What this agent specializes in and when it should be invoked
# many other frontmatter properties
---

Detailed system prompt for the agent describing its role, expertise and behavior.

Format: Codex

repository/
└── .codex/
    └── agents/
        └── reviewer.toml
~/.codex/
└── agents/
    └── reviewer.toml

name = "reviewer"
description = "PR reviewer focused on correctness, security, and missing tests."
developer_instructions = """
Review code like an owner. Prioritize correctness, security, and test coverage.
"""

Format: Copilot

repository/
└── .github/
    └── agents/
        └── agent-name.agent.md
~/.copilot/
└── agents/
    └── agent-name.agent.md
~/.copilot/installed-plugins/<marketplace>/<plugin>/
└── agents/
    └── agent-name.agent.md

---
name: agent-name
description: What this agent specializes in and when it should be invoked
# many other frontmatter properties
---

Detailed system prompt for the agent describing its role, expertise and behavior.

Format: Cursor

repository/
└── .cursor/
    └── agents/
        └── reviewer.md
~/.cursor/
└── agents/
    └── reviewer.md

---
name: reviewer
description: What this agent specializes in and when it should be invoked
model: inherit # "inherit" or a specific model ID
readonly: true # prevents file edits and state-changing shell commands
is_background: false
---

Detailed system prompt for the agent describing its role, expertise and behavior.

Format: Mistral Vibe

repository/
└── .vibe/
    ├── agents/
    │   └── developer.toml
    └── prompts/
        └── developer.md
~/.vibe/
├── agents/
│   └── reviewer.toml
└── prompts/
    └── reviewer.md

agent_type = "subagent" # "agent" (user-selectable) or "subagent" (delegation-only)
display_name = "Reviewer"
description = "Read-only subagent for code review."
system_prompt_id = "reviewer" # must point to a valid prompts/<id>.md

Format: Antigravity

repository/
└── .agents/
    └── agents/
        ├── reviewer.md
        └── developer/
            └── agent.md
~/.gemini/config/
└── agents/
    ├── reviewer.md
    └── developer/
        └── agent.md
~/.gemini/antigravity-cli/plugins/<plugin>/
└── agents/
    └── reviewer.md

---
name: reviewer
description: What this agent specializes in and when it should be invoked
subagent: true
mainAgent: false
model: pro # "inherit", "flash", or "pro"
commandExecutionPolicy: sandbox # "off", "auto", "eager", or "sandbox"
---

Detailed system prompt for the agent describing its role, expertise and behavior.

Format: Devin

repository/
└── .devin/
    └── agents/
        ├── reviewer.md
        └── developer/
            └── AGENT.md
~/.config/devin/
└── agents/
    ├── reviewer.md
    └── developer/
        └── AGENT.md
~/path/to/locally/installed/plugins/<name>/
└── agents/
    └── reviewer.md

---
name: reviewer
description: What this agent specializes in and when it should be invoked
model: sonnet
allowed-tools: [glob, grep, read]
---

Detailed system prompt for the agent describing its role, expertise and behavior.