The model_check.zip file you have requested: Tools and Utilities / Misc / Half-Life Model Validator - 5.19kb is not available. Perhaps try browsing all files for the game Half-Life and upload any files you want to share or are missing. This is the only information we could locate:
Through a hardcoded list of models, it will open the MDL file and parse it client side, tallying up the vertices and bone positions for the entire model and all animations. It will then check this resulting bounding box with some reasonable value.