The nnde package provides a pure-Python implementation of one of the earliest approaches to using neural networks to solve differential equations the trial function method (Lagaris et al., 1998). The nnde package was initially developed as a vehicle for understanding the internal workings of feedforward neural networks, without the constraints imposed by an existing neural network framework. It has since been enhanced to provide the capability to solve differential equations of scientific interest, such as the diffusion equation described here. The ultimate goal of the package is to provide the capability to solve systems of coupled partial differential equations, such as the equations of magnetohydrodynamics.