The GR 5 is well documented. As any GR trail in France, it’s got its own set of guidebooks, consistently edited by the FFRP (Fédération Française de la Randonnée Pédestre which approximately stands for French Hiking Federation). These books are in French and due to the popularity of this route among English speaking (or, in general, non-French speaking) people, UK publisher Cicerone released a guidebook that covers just the Alpine Traverse.