Abstract: A variable-stiffness guidewire system which comprises an elongated flexible guidewire. The guidewire has a body and a guidewire head coupled to the body. The guidewire head is slidably moveable with respect to a guidewire collar of the body to adjust a stiffness of the guidewire. A tool is utilized with the guidewire to engage the guidewire head and move the guidewire head a desired distance from the guidewire collar to achieve a desired stiffness. The tool has a first mechanism that is configured to selectively deploy an insert to be positioned between the guidewire head and the guidewire collar. The insert maintains the desired stiffness of the guidewire.