found it ... works as intended. Thanks a lot!

Looks great. Is there a process I need to follow to enable the feature on the UI or a toggle to switch?

ok ... well .. thanks for taking note as a feat request ;)

Now I understand it. I have to admit that I failed to realize the list feature. The concept seems correct. If I understood correctly it use, the list shows a projection based on tags. That would work as well. As far as I understand the features of UrzaGatherer, tags must be added one by one. The process could be improved by, e.g., having a "convert to list"/"convert to deck" feature at the deck level. Then no need for extra flags or modifying your data model. BTW > thanks for reacting so quickly.

Impressive speed of response. I am not sure I fully understand your question. Let me try. Imagine I have five decks built (no wish for more) but lists for 20, all using one copy of one specific card, which I have four copies of. The UI would now show me a 4 on the bottom left corner and a 20 in the mid of the right side. My perception of this would be that I miss 16 copies of it to finish the decks, while I miss only one given that I never wanted to be able to have all 20 built at the same time. Inspecting this situation with the current UI is cumbersome. For each card in this situation I would have to hover on the card and inspect in which decks the card is needed by looking at the tooltip description triggered by the hovering. By being able to deactivate decks, I would see only a 5 in the mid of the right side, letting me know that my built deck need one extra copy of that card. This situation gets far more aggravated if the number of decks having the card is not all of them but a subset.