A major narrative within the text is the so-called "Osraige Chronicle" (as proposed by Radner) which greatly focuses on the exploits of the ninth century king of Osraige, Cerball mac Dúnlainge, who was the paternal ancestor of the medieval Mac Giolla Phádraig family.
The sole surviving manuscript of the Fragmentary Annals, which is currently held by the Royal Library of Belgium in Brussels, is not in Mac Fhirbhisigh's hand, but in that of an anonymous scribe, who made a fair copy of Mac Fhirbhisigh's text, adding some marginal comments of his own and an index.
Mac Fhirbhisigh's copyist added dates, which he took from the Annals of the Four Masters without troubling to confirm their accuracy or correct them where they were clearly in error.
The original compiler evidently drew upon a variety of sources, some of which (e.g. annals) were probably more accurate and trustworthy than others (e.g. long bardic works).
The fragments combine cold annalistic records with romantic tales and extravagant flights of fancy in a manner that is unique among the Irish annals.