Ogham is an early medieval script, typically consisting of strokes and notches cut along the edge or face of a standing stone, used mainly to record personal names in early Irish. Most ogham stones carry one inscription; this one carries three, and the relationship between them is far from straightforward.

The stone was not always at Coolmagort. It formerly lay in the chancel of Kilbonane Church before being moved to its present location, where it is displayed alongside seven other ogham stones recovered from a nearby souterrain, an underground stone-lined passage associated with early Irish settlement. The scholar R.A.S. Macalister examined it in both 1903 and 1945, and his readings remain the principal source for what the inscriptions say. On the face of the stone, he read a main inscription and a smaller secondary line beside it, transcribed as NIR*** MN[I]DAGNIESSICONIDDALA AMIT BAIDAGNI, with gaps where the stone is damaged at a repaired break across its middle. On the right-hand edge, or dexter angle, he read B[AID]AGNI MAQI ADDILONA, a formula using the common ogham word MAQI, meaning "son of". On the left-hand edge, or sinister angle, he read NAGUNI MUCO BASIDANI. Crucially, Macalister concluded that the face inscriptions are independent of those on the edges, suggesting the stone may have been inscribed on separate occasions, or by different hands, with different purposes in mind. The stone has since been documented as part of the Ogham in 3D project run by the School of Celtic Studies at the Dublin Institute for Advanced Studies, which uses photogrammetry to produce digital models of ogham stones across Ireland.