In the USA, there are three varieties of "diet" Cool Whip: Cool Whip Lite, Cool Whip Free, and Cool Whip Sugar Free
I found some info on the kraft foods website
You can see which matches your ingredient and/or nutrition label.
The light and the sugar free have 3g of carbs, 0g, of protein, and 1g of fat and 20 calories (per 9g serving)
The free has 3g of carbs, 0g, of protein, and 0g of fat and 15 calories (per 9g serving)
The nutrition information is so close, that I personally would consider them all virtually interchangeable. For that matter, regular Coolwhip only has 25 calories per 9g serving and is actually lower in carbs (1.5g of fat, and 2g of carb, and 0 protein).