Abstract: A device for measuring and monitoring tools of a machine tool, wherein the machine tool comprises a spindle shaft for the tool, the shaft being arranged in a spindle housing, wherein a work piece with good electric conductivity can be machined using the tool, wherein the spindle shaft is electrically insulated from the spindle housing, includes a measuring and monitoring system. The measuring and monitoring system measures at least one electric measurement, which depends on the contacting state between the tool and the work piece. A rotary transmitter contacts the rotating spindle shaft to measure the measurement detectable between the tool and the work piece, wherein the rotary transmitter is connected with the spindle housing in an electrically insulated manner.