Codex is OpenAI’s AI agent. You can use it in three ways: as a CLI in the terminal, as a desktop app, or as the ChatGPT/Codex extension in VS Code, which the welcome page of MainPath extension links to directly. The MainPath Toolbox installs the CLI and the desktop variant during developer setup.
Starting
For the CLI, change into the project folder and run codex. As with every agent, open the parent project folder so that all repositories are visible.
cd ~/Documents/MainPath/<organization-slug>/<project-slug>
codex
Preconfiguration
MainPath rules come from the mp CLI agent plugin. mp agent install places the plugin and skills under ~/.codex/ and writes the MCP server application-platform into ~/.codex/mcp.json. Codex therefore knows platform conventions from the start: applications start via mp run-local, .gitlab-ci.yml and env/*.generated.env are managed by MainPath, and custom values belong in env/*.custom.env. Project-specific additions go in an AGENTS.md in the application repository; how that works is described in Your own rules for AI agents.
Install the agent plugin
mp agent install
mp login
A separate marketplace entry is not required. If the mp CLI is not signed in yet, run mp login and restart Codex. All installation routes, the list of MCP tools and the typical failure cases are described in CLI and agent plugin.
A prompt such as “Create a new MainPath project with a Flutter app and a FastAPI backend and clone it.” is enough from then on; the flow behind it is described in Create a new project.