Any artisan’s tools or miscellaneous tools can be purchased as a masterwork version for an additional cost of 150 gp. The only function of masterwork tools is to negate disadvantage imposed by the complexity of a subject, project, or product, if it could offset by higher-precision tools or by a wider-than- normal array of supplies. This effect applies at the Dungeon Master’s discretion; not every situation that imposes disadvantage can be offset by masterwork tools.
For example, as part of a forgery attempt, a character is trying to imitate a precise shade of ink used in military documents. The purpose of this ink, with its odd mixture of pigments, is to deter just this sort of forgery! Normally, the DM would impose disadvantage, but decides that the wider array of inks available in the character’s masterwork forger’s kit is enough to prevent that penalty.