Basically, I’m making my own specific system for an inventory and every time I pick up a new item and keep that item selected, and then try to pick up another item (my pickup system is by clicking a part that gives you the item), it won’t pick it up. Might be a bit confusing but whatev’s.
Basically basically, how do I the left click’s priority ClickDectector’s > tool’s even if there’s nothing in the tool?
if you’re asking how to click parts over activating a tool, i thought of a stupid way to do this, maybe even a terrible way to do this but it’ll get you somewhat moving in the right direction
you would need to check Mouse.Target and see if there is a ClickDetector in the target, then in the tool handler, add some logic in tool.Activated where if there is actually a ClickDetector , it doesn’t activate. i know it’s not the best solution but hopefully someone more experienced in this could help you 
You can’t. Robot doesn’t have a way to do this built in. There are hacky ways around this though. The above response will work, but my take if I have to hack together robloxs events would be to make a module where I register functions into as well as the trigger and I would bind a new ‘thisframe’ request to the trigger that just says that this event was attempted activated. Everything that wants to activate (click detector and tool) would register interest, and then you would have a denounced task.defer that will look at the highest priority registered interest and run the function associated with that. Now you have a reusable system.
Though if we are going that far anyways I just flat out recommend making your own input management system which is simpler overall.