The repairable attribute is an item-only attribute that allows you to repair a damaged tool. Usually, this attribute will be used for the normal item type. By default, repairable is set to false so you only have to set this if you want to be able to repair the item. The maxuses attribute, while not required, should be included in your item properties because there is no point being able to repair an item if it can never receive damage in the first place. Here what the repairable attribute should look like in the item file.
maxuses = 64; repairable = true;
By default, items do not receive damage from any normal actions. Events must be coded for an item for it to be damaged. Refer to the maxuses page for information about how to make a tool get damaged.