How can I make it where a player is limited to 1 of each tool?

How can I make it where a player is limited to 1 of each tool?

Just check it with :FindFirstChild() everytime the server gives the player a new tool/item Example:

local toolName -- your tool name from remote event/function or something else
local hasTool = player:WaitForChild("Backpack"):FindFirstChild(toolName)

if hasTool then
   warn("player has " ..toolName.. " already!")
else
   -- do whatever you want
end

You can make it so it checks if the player already has that tool for example:

local tool = game.ReplicatedStorage.Tools:WaitForChild("BloxyCola") -- This is just an example

function giveTool(Tool, plr)
	if not plr.Backpack:FindFirstChild(tool) then
		Tool:Clone().Parent = plr.Backpack
		-- Do whatever you want
	else
		warn(plr.Name.." already has "..Tool.Name.."!")
		-- Do whatever you want
	end
end

-- The function must be connected to some kind of event for example
game.Workspace.GiverPart.ClickDetector.MouseClick:Connect(function(playerThatClicked)
	giveTool(tool, playerThatClicked)
end

You can also do it like this

local tool = game.ReplicatedStorage.Tools:WaitForChild("BloxyCola") -- This is just an example

game.Workspace.GiverPart.ClickDetector.MouseClick:Connect(function(plr)
	if not plr.Backpack:FindFirstChild(tool) then
		tool:Clone().Parent = plr.Backpack
		-- Do whatever you want
	else
		warn(plr.Name.." already has "..tool.Name.."!")
		-- Do whatever you want
	end
end

All of this was an example so you should use your imagination and modify the script to your needs but hopefully I helped and you understood what I tried to tell you.

But if this was too complex to you then you can either research more about the things on this script, search for a simpler method or check other answers by other users or if you have any other problem just ask me.