The Line Tool is introduced during the tutorial level Equilateral Triangle. When active, the tool creates lines by a straight-edge; either by two consecutive clicks to the two endpoints of a segment, or by clicking on the first point and dragging to the second. When selecting an endpoint, the tool tries to favor nearby intersections between lines (whether straight lines or the circumference of a circle) or points previously marked with the Point Tool; however, it is also possible for an endpoint to be placed on a free point.
The Line Tool costs one elementary move if it creates a new line or if it is used on an existing line segment or ray to extend it into a line. There is no cost for trying to re-create a line that has already been constructed.