KiPadCheck can check drill-drill spacing. I’m also working on DRC Load / Save. That thread contains reference to EAGLE DRU files. In particular the layer definitions section (shown is two copper layers): (these are EAGLE DRC screenshots):
And the REST-RING section with DRC rules for inner/outer/top/bottom annular rings for pads/vias/uvias.
And the sizing for drill sizes:
My belief is that the layer thicknesses are specified exactly because the Blind Via Ratio check here. I don’t see anywhere else that would be useful (besides the 3d viewer).
I am trying to figure out what makes sense to implement in KiPadCheck.