The Naeshi-eunuchs were essentially servants who served the King and the Royal family members inside the palace. They were emasculated males and were also viewed as private house slaves, but in fact they were officially designated personnels of the government as well, who were attached to the Nashi-bu office.
They were in charge of serving food prepared for the King and the Royal family, relaying the King's order to related persons or offices, timely opening and closing the gates of the palace, and also keeping the inside of the palace clean, Yet, at the same time they were also required to be equipped with certain level of linguistic abilities in terms of Chinese letters and also Confucian sensibility. In fact they had to go through certain tests for such skills on a regular(monthly) basis, and were promoted according to the number of their service days. Needless to say, they were outranked by the regular officials, but they also had a higher authority than the Jabiik/雜職 officials who had to attend to actual matters involving management of commodities or facilities.
The rank" for the Naeshi-eunuchs ranged from the Jong 2nd-pum/從二品 grade to the Jong 9th-pum/從九品 grade. One seat arranged by the government was occupied by several personnels who were assigned to various responsibilities, which shows that the Naeshi-eunuchs were regulated by the Chaea-jik/遞兒職. practice(Rotating personnels in services).
The number of Naeshi-eunuch personnels were 140 according to the Code of Laws {Gyeongguk Daejeon/經國大典}, then increased to 160 during the 15th and 16th centuries, and again rose to 184 during the later days according to the {Daejeon Tongpyeon/大典通編}, and finally to 264 according to the (Yukjeon Joryael /大典條例} which was issued in the ending days of the Joseon dynasty. Partial reason for this increase was the increase in the number of residents living inside the palace itself, but more importantly it was due to the changes made in the Naeshi-eunuch personnels' working conditions and forms.
The Naeshi-eunuchs, being in a position ordered to relay the King's orders to the rest of the government and serve the leader of the country in a very close proximity, were also in a potential position to bond themselves with huge political power. But usually, in most cases they were restrained and regulated by the government during the Joseon dynasty period. They were, after all, in charge of the day-ta-day aspects of the King and the Royal family members. They were shadows of the King, occupying both an official and a private position, and also a dual nature of such sort.