The best tool for digging in clay soil is a sharp and sturdy digging spade. Clay soil can be dense and compacted, making it challenging to dig through. A digging spade with a sharp, pointed blade and a strong handle allows you to penetrate the clay effectively. The sharp blade helps to break through the compacted soil, while the sturdy handle provides leverage and strength to lift and turn the clay. Additionally, a spade with a long handle allows you to maintain an upright posture while digging, reducing strain on your back. By using a quality digging spade, you can make the task of digging in clay soil easier and more efficient.