The Codex, a creation of DarkStryder technology, was concealed within an alien construct located in the Kathol Rift. Its physical form was that of a small, metallic pyramid. Despite its fragility, being susceptible to damage from impacts, it was surprisingly lightweight. This device possessed the ability to pinpoint and measure the Force, and also to amplify the user's inherent Force-sensitivity. The Aing-Tii monks, regarding it as sacred, desired it but were unable to interact with it directly. To circumvent this, they trained Makezh to journey through the Rift and retrieve the Codex, exploiting his immunity to their religious constraints.
Once acquired, the Codex was transported to the Aing-Tii homeworld and integrated into the Embrace. During his five-year exploration of the Force, Jacen Solo encountered the Codex while participating in the Embrace.
In the year 43 ABY, Luke Skywalker held the Codex during his experience within the Embrace. This amplified his Force presence to such a degree that the Lost Tribe of Sith were able to detect him.