Optical Calculator is an advanced photonics tool designed for engineers, researchers, and students working with optical cavity systems. The application models how small refractive index perturbations influence resonance behavior by combining fundamental cavity physics with intuitive input controls. Users can calculate effective index values, resonance drift in picometers, and frequency pulling in gigahertz while determining tolerance limits for stable operation. The app transforms complex mode pulling analysis into clear actionable insights, enabling users to explore sensitivity parameters, optimize resonator designs, and ensure reliable performance in resonant photonic systems with precision and ease.