Codex/Subagent
- Codex's implementation of AI/Agent/Subagent. Custom agents are standalone TOML files in
~/.codex/agents/ for personal scope or .codex/agents/ for project scope. - Required keys are
name, description, and developer_instructions. A file may also carry config.toml keys including model, model_reasoning_effort, sandbox_mode, mcp_servers, and skills.config. - Subagent activity surfaces in the ChatGPT/App/Desktop, Codex/CLI, and the IDE extension, and Codex/Hook exposes
SubagentStart and SubagentStop. - Standalone configuration and plugin packaging are separate surfaces. Build plugins documents
skills, mcpServers, apps, and hooks in the manifest and no agents — so a Codex/Plugin cannot ship one of these, even though the host runs them. "Does tool X support subagents" is the wrong question.