With canning season coming up quick, if not started already for some folks. Here is this months idea. Go through your jars now. Wash and check for cracks and chips, discard bad jars and buy new ones to replace the "bad" jars.
You do not want to use chipped jars, as they will not seal properly. Do not use old heirloom jars, as they will not seal properly either. If a jar is cracked it can shatter while in the canning process and make a big mess and you not only lose a jar, but product as well.
Good luck and happy canning!