> For the complete documentation index, see [llms.txt](https://docs.erathos.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.erathos.com/api/concepts.md).

# Concepts

- [Authentication](https://docs.erathos.com/api/concepts/authentication.md): Create and use an API Key.
- [Metadata](https://docs.erathos.com/api/concepts/metadata.md)
- [Rules](https://docs.erathos.com/api/concepts/rules.md)
- [Variables and secrets](https://docs.erathos.com/api/concepts/variables-and-secrets.md)