Abstract: A guide tool assembly is provided for use with a tape measuring device to measure, scribe or cut drywall or the like. The guide tool assembly consists of two parts, one a slidable guide element including a mounting slot for enabling the slidable guide element to be slidably mounted on the measuring tape of the tape measuring device and a knife guide element adapted to be affixed to the measuring tape at the free end thereof. The knife guide includes a transverse opening therein for, in one application, receiving a cutting blade. In this application, the slidable element is set at the desired measuring point along the tape and with the slidable element in engagement with the edge of the drywall panel to be cut, the slidable element and the cutting blade are moved in parallel to provide a cut of the desired width. In an alternative embodiment, the assembly is used for making arcuate cuts or inscriptions.