Abstract: The present invention is a tool that quickly and accurately places joist hangers on headers to prepare the headers for the installation of joists. The tool has a lower flange which includes a transverse slot. An upper flange on the tool has two recesses spaced apart along a forward face of the upper flange. The recesses and the transverse slot cooperate to engage and constrain the joist hanger during installation. The tool also includes a handle member with a grip portion located remotely from the main body of the tool. The handle member allows an installer to position and install the joist hanger without exposing his hand to the area of installation.