All the error from json.Unmarshal says is "cant Unmarshal {" or whatever character it's failing at. With a large enough JSON file, it can be very difficult to figure out where the malformation is.
I'd like to find a way to get a more specific location, using a combination of functions supported by the json library or others. One possibility can be the line and character number of the failure. I'd also be happy to get the tree path to the malformation.