FIG. 1 is a bottom front perspective view of a paintbrush holder tool showing my new design. FIG. 2 is a side elevational view thereof; FIG. 3 is a bottom plan view thereof; FIG. 4 is a rear elevational view thereof; FIG. 5 is a top plan view as viewed from the bottom in FIG. 4. FIG. 6 is an end elevational view as viewed from the left of FIG. 4; and, FIG. 7 is an opposite end elevational view as viewed from the right of FIG. 2.