Contacts.app - list all groups a contact is in Is there a possibility to list all the groups, a contact is in, on the card.
This would make the organisation of my contacts much easier
My solution doesn't list the groups on the contact card itself, but it may still solve your situation:

By holding down the "Option" key when you have a contact selected and the "Groups" pane showing, the groups which contain the selected contact are highlighted.

Related:


Highlight the groups a contact is in?