A modular hydro jetting tool for fracturing well formations the tool has a plurality of jetting modules. Each jetting module has a plurality of jetting nozzles therein. A sleeve disposed in each jetting module except the lowermost module, and each sleeve is moveable from a first position covering the jetting nozzles in the corresponding module to a second position covering the jetting nozzles in an adjacent module. Plugs may be pumped into the tool to move each sleeve sequentially, thereby operating the jetting modules sequentially