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

# Problems

This reference lists the custom [problem types](/technical-overview/api-design-guide/errors.md) that our APIs use.

## Standard http problems

* [400 Bad Request](https://httpstatuses.io/400)
* [401 Unauthorized](https://httpstatuses.io/401)
* [403 Forbidden](https://httpstatuses.io/403)
* [404 Not Found](https://httpstatuses.io/404)
* [500 Internal Server Error](https://httpstatuses.io/500)

## Custom problems

* [400 Validation Failed](/reference/problems/validation-failed.md)
* [403 Bad Subject](/reference/problems/bad-subject.md)