Using even a simple tool like a pointing stick to point on a board is not trivial. An individual's brain has to first recognize the stick's size, shape and dynamics, locate its target in the visual and body coordinates, integrate this information with the stored body representation, before finally calculating the changes in limb angles required to make the movement to touch the target. It is generally accepted that the human dexterity with tools, which requires proficiency in the above complex and error prone calculations, stems from our ability to incorporate and use tools as extensions of our body. However, regularly examined tool incorporation processes are gradual and result from extended tool-use. On the other hand we can immediately switch between tools, say from pointing on a board with the pointing stick to pointing with a much shorter pen without requiring any practice. This ability points to the presence of immediate tool incorporation processes. Here, utilizing two novel experiments, we elucidate the presence of additional immediate tool incorporation effects that determine motor planning with tools. Interestingly, tools were observed to immediately induce a trial-by-trial, tool length dependent shortening of the perceived limb lengths, opposite to observations after extended tool-use. Our results thus indicate that tools induce a dual-effect on our body representation; an immediate shortening that critically affects motor planning with a new tool, and the slow elongation probably representing the increase in skill of a repeatedly used tool.