A carpenter's deck board and fastener positioning tool has a first, proximal part which rests temporarily on the top of a joist, and a second, distal part which rests temporarily on the top of a deck board to be installed. The first, proximal part has a pair of spaced-apart, downwardly extending tabs, one for extending along each side of the joist. This way, when the tool is placed on the joist, the tabs center the tool on the joist. The second, distal part is a longitudinal, substantially flat plate extending from the first, proximal part parallel to the joist, for resting on top of the deck board to be installed when the board is resting transversely on the joist. On or in the flat plate are fastener placements for enabling or indicating the proper location of fasteners for effectively connecting the deck board to the joist.