What tool is primarily used for zesting citrus fruit?

The tool primarily used for zesting citrus fruit is a zester or microplane. This specialized tool is designed with sharp, fine holes that allow it to remove only the outermost colorful layer of the citrus peel, known as the zest, while avoiding the bitter white pith underneath. The microplane's design makes it easy to create fine, fluffy zest that can enhance the flavor of various dishes and cocktails, providing a burst of citrus aroma and taste.

In contrast, while a grater can be used for zesting, it is not as precise as a zester or microplane, potentially leading to the inclusion of unwanted pith. A paring knife is primarily used for peeling and slicing fruits and vegetables but is not ideal for zesting due to its lack of a focused zesting capability. A peeler, generally used for removing the skin from fruits and vegetables, is also not suited for extracting zest effectively. Therefore, the zester or microplane stands out as the most appropriate and effective tool for achieving the perfect citrus zest.