web.de is a German Internet portal which also provides an email service, address books and calendars.
CalDAV base URL: https://caldav.web.de/
User name and password: your web.de user name and password
Choose "Login with email address", and enter your web.de email address and password.
You can also use the base URL https://carddav.web.de and your web.de email address and password.
No CardDAV contact group support. Choose "per-contact categories" as contact group method to minimize problems.