Sensipy simulates gamma-ray follow-up observations of time-variable astrophysical sources using a Python toolkit built on top of gammapyn (ascl:1711.014). It calculates differential and integral sensitivity curves from instrument response functions and spectral models, and estimates the exposure time required to detect a source with a given spectrum at a specified significance level. Sensipy supports multiple gamma-ray observatories, provides follow-up utilities and lookup tables for quick assessments, includes extragalactic background light absorption models, and provides workflows that load IRFs, apply EBL attenuation, and generate detectability curves under different observing conditions.