--To you this script make a local script and put it in starterGUI

--[[
	Put me in StarterGui or StarterPack :)
]]
local Player = game.Players.LocalPlayer
repeat wait() until Player.Character -- Yield until the Player's Character is no longer nil
local Character = Player.Character
local Humanoid = Character:WaitForChild("Humanoid")
local UserInputService = game:GetService("UserInputService")
local currentJump
local debounce = true
local DoubleJumpVelocity = 100 -- 50 is a normal ROBLOX jump

function jumpRayDown()
	local nR = Ray.new(Character.Torso.Position,Vector3.new(0,-1,0).unit*4)
	local hR,pR=game.Workspace:FindPartOnRay(nR,Character)
	if hR~=nil then
		return true
	end
	return false
end

Humanoid.Changed:connect(
	function(Property)
		if Property == "Jump" and debounce == true and Humanoid.Sit==false then
			currentJump=true
			debounce = false
			newConnection = Player:GetMouse().KeyDown:connect(function(key)
				if key:lower():byte()==32 and currentJump and Character.Torso.Velocity.y>-30 then
					currentJump=false
					for i, v in pairs(Character:GetChildren()) do
						if v:isA("BasePart") then
							v.Velocity = Vector3.new(v.Velocity.x,DoubleJumpVelocity,v.Velocity.z)
						end
					end
				end
			end)
			spawn(function()
				repeat wait() until jumpRayDown()==true
				debounce = true
				currentJump = false
				if type(newConnection)=="function" then
					newConnection:disconnect()
				end
			end)
		elseif Property == "Jump" and Humanoid.Sit==true then
			Humanoid.Jump=false
		end
	end
)