Synology DiskStation Manager (DSM) is a Linux based software package that is the operating system for Synology's DiskStation and RackStation products. A CalDAV server is available in the base system. CardDAV can be installed as an extra package. It's also possible to run other CalDAV/CardDAV software like Baïkal and ownCloud on Synology systems. In this case, see the respective configuration pages for details.
The Calendar package provides a calendar with Web and CalDAV interface.
You can view the CalDAV URL in the Calendar Web interface (Calendar > CalDAV Account). Use the macOS / iOS URL.
So, the CalDAV Base URL could look like this:
Note: In previous Synology DSM versions, CalDAV was served using the WebDAV server package (default ports 5005/5006). This method is now obsolete. Make sure that you don't have enabled CalDAV in the WebDAV server package when you use the new Calendar package. If you don't need WebDAV for file access, you can completely uninstall the WebDAV server package.
The CardDAV Server package provides a CardDAV server with address book backend in the Web interface.
CardDAV Base URL:
User name and password: same as for Synology DSM
Contact group method: groups are separate VCards
Only applies to the legacy WebDAV/CalDAV server package: If you're accessing a newly created calendar/task list, Synology returns 404 Not Found when this collection is queried by DAVdroid. To work around this, add an event and a task to the calendar (e.g. with DAVdroid). Then synchronize and the 404 error should be gone. If possible, use the new Calendar package on your Synology device to avoid this problem.