# App reference

> The details you look up while building an app. Configuration keys, Bashio functions, files, the runtime environment, and the security rating.

Source: https://contributors.home-assistant.io/apps/reference/

The pages in this section are for looking things up. For the why and the how, start with the [guides](https://contributors.home-assistant.io/apps/guides/).

- [App configuration](https://contributors.home-assistant.io/apps/reference/configuration/): every key of `config.yaml`.
- [Bashio](https://contributors.home-assistant.io/apps/bashio/): every function of the shell library in the base images.
- [App files](https://contributors.home-assistant.io/apps/reference/files/): the files in an app folder and in a repository.
- [Runtime environment](https://contributors.home-assistant.io/apps/reference/environment/): what your container gets from the Supervisor: environment variables, folders, and network addresses.
- [Security rating](https://contributors.home-assistant.io/apps/reference/security-rating/): how the Supervisor computes the rating users see.
- [Supervisor API](https://contributors.home-assistant.io/apps/supervisor-api/): the endpoints your app can call.