Gmsh is an open source 3D finite element mesh generator with a built-in CAD engine and post-processor. Its design goal is to provide a fast, light and user-friendly meshing tool with parametric input and flexible visualization capabilities. Gmsh is built around four modules (geometry, mesh, solver and post-processing), which can be controlled with the graphical user interface, from the command line, using text files written in Gmsh's own scripting language (.geo files), or through the C++, C, Python, Julia and Fortran application programming interface.