<p>Reducing lattice thermal conductivity (<i>κ</i>_<i>latt</i>) is essential for advancing thermoelectric materials. Achieving this requires deeper insight into how microstructural defects influence phonon scattering and the ability to model these interactions effectively via the Debye–Callaway model. However, the mathematical complexity of its nonlinear integral form has historically limited its use to specialists with advanced coding skills. In this study, we present a comprehensive review of the Debye–Callaway model, emphasizing the physical parameters governing nine key phonon scattering mechanisms. Building on this, we introduce a novel, standalone simulation program with an intuitive, slider-based graphical interface that enables real-time visualization of how variations in microstructural parameters affect <i>κ</i>_<i>latt</i>. The tool features editable inputs for experimental datasets, temperature ranges, and material-specific parameters, with instant graphical feedback. Through three case studies, we demonstrate its capabilities in deconvoluting defect contributions, identifying modelling errors, and predicting defect impacts, providing a significant advance in phonon transport analysis.</p><p></p>