The Otto's rise to prominence as Florence's chief criminal magistracy, with wide jurisdictional competence in the city itself and its subject territories, did not occur immediately at its founding in 1378. Instead, its original mission was to conduct surveillance. A factional battle, known as the Ciompi Revolt, was then being waged for the control of the government by elements of the oligarchy, small shopkeepers, and clothworkers who were not represented by a guild. Created on 2 September 1378, the Otto di Guardia began as an ad hoc executive committee with extraordinary powers. The merchant-diarist Goro Dati explains its original duties:

It is clear, then, that the Eight began as a political police during an extremely turbulent moment in Florentine political history. Reflecting the movement toward the equalization of political power that occurred just after the revolt (and that ended in 1382 with the oligarchical restoration), appointment to the office was equally divided between the seven major and the fourteen minor guilds. Its elected members reported the results of their investigations to the Signoria (the highest executive authority of government) in secret.