Abstract: A tool for assisting in the installation of horizontally overlapping siding boards for the exterior of a building including a body member and a gate member rotatably attached thereto. The body member has a head portion that forms a downwardly facing channel for hooking onto the upper edge of a siding board, and a mid portion that coacts with the head portion and the gate member to form an upwardly facing channel for receiving the lower edge portion of a siding board to be installed on the building. The gate member is moveable between open and closed positions whereby when installation of the siding board is completed, the gate member can be rotated to an open position for removal of the tool.