The Gunsmith is an information role that can target a player at Night to learn if they have a gun in flavor. Members of the Mafia (that are not Doctors), Cops, FBI Agents, Vigilantes, other Gunsmiths, Paranoid Gun Owners, etc. all have guns in traditional flavor. Notably, Serial Killers and Doctors do not have guns.
Gunsmiths are usually, but not necessarily, pro-Town. They are considered somewhat weaker than standard Cops and are usually included in setups where they can get positive results on players who are not Mafia-aligned.
The name "Gunsmith" is also occasionally used for a Psychologist, but this terminology is almost unheard of on mafiascum.net (it's more commonly seen on other sites).
In Normal games on mafiascum.net, a Gunsmith gets guilties on all Mafia (except Traitors and Doctors), Cops, Vigilantes, Gunsmiths, Role Cops, Vanilla Cops, PT Cops, Vengefuls, Detectives, Neapolitans, Backups of roles with guns and JoATs that have any of these listed powers.