Population Synthesis Toolkit (PST) facilitates reproducible, customizable modeling of galaxy spectral and photometric observables in extragalactic astrophysics. It synthesizes stellar populations using a variety of simple stellar population (SSP) models to compute observable quantities such as integrated spectra, broadband photometry, and equivalent widths from synthetic or observed data. The code combines individual SSPs with user-defined star formation and chemical evolution histories to simulate composite stellar populations and derive their spectral energy distributions across wavelengths. PST includes a flexible interface to handle multiple SSP libraries, assemble composite populations, and calculate synthetic observables for galaxy models, with optional modules for dust extinction and kinematics effects.