> For the complete documentation index, see [llms.txt](https://doorkeeper.gitbook.io/guides/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doorkeeper.gitbook.io/guides/internals.md).

# Internals

- [Database Design](https://doorkeeper.gitbook.io/guides/internals/database-design.md)
- [Internationalization (i18n)](https://doorkeeper.gitbook.io/guides/internals/internationalization-i18n.md)
- [Rake](https://doorkeeper.gitbook.io/guides/internals/rake.md)
- [Testing](https://doorkeeper.gitbook.io/guides/internals/testing.md)
- [Upgrading](https://doorkeeper.gitbook.io/guides/internals/upgrading.md)
- [Creating extensions](https://doorkeeper.gitbook.io/guides/internals/creating-extensions.md)