Each module comes with its own documentation. Currently, in places this can be quite minimal but we are continuously working to improve this. Soon we have have direct links to the Mathematica documentation here, as well as links to the documentation for other key modules.
We wil also soon have a list of conventions used throughout the Toolkit.
One of the aims of the toolkit is for all components to be well-tested and reliable. Every commit is tested using a Jenkins continuous integration server. This means each time the code is changed it is automatically tested to ensure no errors have been introduced. You can find the current build status at build.bhptoolkit.org.