A smithing template defines a tooltip for an item to use as an upgrade for another item. These smithing templates can be found in a data pack under the smithing_template folder in a namespace. Note that a smithing template does not determine whether an item may be used to transform or modify an item stack, since that is handled by recipes instead. It is purely used for the tooltip of an item. This likely won't change as to not break any existing custom smithing recipes. The smithing template type is determined by the type field, and all types are found in the sidebar.