RadiaBeam has developed and built a Bunch Shape Monitor (BSM) prototype for measuring the longitudinal bunch distribution in hadron linear accelerators. The device has been designed to operate at 402.5 MHz and it incorporates three main innovations to improve its performance: a focusing field between the target wire and the entrance slit for better collection efficiency, a novel design of the RF deflector to enhance beam linearity, and a moving mechanism that allows shifting both the wire and deflector cavity to enable transverse profile measurements. The BSM prototype has been installed at the Beam Test Facility at the Spallation Neutron Source and is currently under testing for characterization. In this paper, we will present the design, fabrication, and first test results of the BSM prototype.