The present invention relates to a device for tensioning or de-tensioning tools, having a tool shaft in a tool chuck which has a sheath section open on the free end thereof and which is made of electrically conductive material, for receiving the tool shaft in a friction connection, having an induction coil which surrounds the sheath section of the tool chuck, to which preferably high-frequency alternating current can be applied, and which is designed as a ring or cylinder coil, wherein the device has at least one channel running between the inner peripheral surface of the induction coil and the sheath section of the tool chuck, through which flows a cooling agent which cools the sheath section of the tool chuck.