WRL files are created by tool when it encounters fatal or warning-level geometry issues during model compilation and lightmapping (e.g. open edges, nearly coplanar faces). These files can be reimported back into the user's 3D software to visualize where problematic edges or faces are present and correct them before reattempting model compilation.
Unlike Halo 1 Tool's WRL 1.0 files, the WRL files exported by H2 Tool are VRML 2.0. While Blender has some support for the 2.0 version, you may still require older software to import these files. Luckily they aren't nearly as important as they are in CE since Sapien displays level errors for you.
The WRL ("world") file format is not Halo-specific, but rather a 1997 industry standard called VRML 2.0. They consist of a list of
Separator nodes, one for each error found by Tool. The file always begins with the comment
#VRML V2.0 utf8.