Is there any way to test if a Players inventory is not full in Minecraft

Solution 1:

I found /testfor @p {Inventory:[{Slot:0b}]}, which outputs a 1 block signal if there's an item there, and no signal if that slot is empty. This would require 36 command blocks, to check every slot (including the hotbar; 27 to just check the inventory, 40 if you wanted to check armor slots)

Solution 2:

This solution works for 1.14 for sure, I have not tested for 1.13. It can be elaborated on to check the entire inventory in one command; however, in this example I am only checking the hotbar.

/execute if entity @p[nbt={Inventory:[{Slot:0b},{Slot:1b},{Slot:2b},{Slot:3b},{Slot:4b},{Slot:5b},{Slot:6b},{Slot:7b},{Slot:8b}]}] run say Hotbar is not full.