Synthesizer generates synthetic astrophysical observables from theoretical models and galaxy formation simulations. The software produces spectra, photometry, images, and spectral cubes from analytical descriptions or particle-based simulation outputs. Modular components provide capabilities for stellar population synthesis, photoionization modeling, dust attenuation, and observational imaging configurations. These tools support the creation of mock observations, including imaging and integral-field spectroscopy. Synthesizer allows users to explore how modeled observables depend on physical assumptions and parameter choices within forward-modelling workflows.