What bar tool is primarily used for stirring cocktails?

The bar spoon is specifically designed for stirring cocktails, making it the correct choice for this question. Its long handle allows bartenders to reach deep into mixing glasses or shakers, facilitating efficient mixing of ingredients without splashing. Additionally, the spoon's shape and design help in evenly combining ingredients, especially when dealing with heavier liquids, while the twisted handle can also aid in more controlled stirring.

The shaker, while an essential tool for mixing cocktails, is primarily used for shaking, which is a different technique than stirring. A jigger is employed for measuring liquids, crucial for recipe accuracy but not for the physical act of stirring. Lastly, a muddler is utilized to crush fruits or herbs to release their flavors, which is also distinct from the stirring process. Each tool has its own specific purpose in cocktail preparation, but in the context of stirring, the bar spoon is the most appropriate choice.