Visualization Toolkit is a software system for computer visualization.
There are two kinds of VTK formats. One is VTK legacy format, which can be edited as easily as txt file, the other is based on XML, which need us to know more about XML format.
More detials can be found in The VTK User’s Guide 11th Edition
Tecplot is a post-process software. One of the data file format is modularized .dat file.
Convert the .dat file to vtk file.
Python, and the package pyevtk.
In future, a module in C++ will be developed to generate the vtk file directly from output of model, rather than .tec file.