A diffeomorphism is a continuous bijective function, a mapping from a point in one manifold to another. This lets you see if your given function is a diffeomorphism between two surfaces defined in 2-variate space. A diffeomorphism is usually defined as a function, usually with a greek letter phi or psi. We define it as f:M->N, where M and N are manifolds, in this simple case, it does not matter if they are endowed with a metric, or if that metric is endowed with a connection. Not all functions are diffeomorphisms, they have to be bijective, meaning there has to be a one-to-one correspondence between points, and it and its inverse have to be continously differentiable, meaning the map from M to N is continously differentiable, and so is its inverse N to M. Two manifolds with a function that is a diffeomorphism are diffeomorphic manifolds, and are a (or C^a) diffeomorphic if said function(s) are a-times continously differentiable, as is its inverse a-times conitnously differentiable. I developed DiffeoCheck as a personal tool to aid my studies, as well as a tool for others. DiffeoCheck uses numpy. In order to verify bijection, the program computes the Jacobian and its determinant, and verifies its positivty throughout the domain. The try block is used to handle exceptions, as well as to compute partial derivatives. Although this is mainly to verify differentiability, it may also indirectly verify continuity through the inferred existence of partial derivatives. This is a weak check, and I may write new code to fix it. The user enters two surfaces, as well as a function, and it computes whether it is a diffeomorphism or not.