Incorporating passive systems, such as louvers, into building design can significantly reduce energy consumption and carbon footprint by maximizing natural ventilation and daylighting, thereby reducing reliance on mechanical climate control systems. In this article, we present a novel decision support tool designed to optimize the sizing of louvers in hot and humid climates, considering solar protection, light efficiency, and energy gain. Using three performance coefficients (Cm, CLD, and CECC) and two performance labels, the tool enables architects and engineers to make informed decisions on louver dimensions, material selection, and orientation. Through a series of case studies, we demonstrate the tool's effectiveness in improving louver performance and energy efficiency while maintaining occupant comfort. This innovative approach offers valuable insights for sustainable building design in challenging climatic conditions. Highlights • Development of a decision support tool for determining optimal louvers size in hot and humid climates that considers solar protection ("Cm"), light efficiency ("CLD"), and energy gain ("CECC"). • Louvers efficiency evaluation uses three coefficients to determine their effectiveness in optimizing solar protection, daylighting, and building energy efficiency. • Development of a simplified, user-friendly tool for design offices and architects to optimize solar protection and daylight efficiency in buildings without using simulation software.