The Living Record
Kōyilolugu (Tamil: kōyil = temple + olugu = procedure/record) is the meticulously maintained chronicle of a major Śrī Vaiṣṇava temple. It records: the temple's founding mythology, the list of Ācāryas and trustees who served it, the details of land grants and endowments, the prescribed schedule of daily worship, the procedure for each festival, and significant historical events.
The Śrī Raṅgam Kōyilolugu
The Kōyilolugu of Śrī Raṅgam is the most famous such record, compiled and updated by the temple administration over many centuries. It is an invaluable source for understanding the liturgical life of the temple, the history of the Śrī Vaiṣṇava community, and the specific ritual procedures (niyamas) that govern worship at Śrī Raṅgam.
Significance
The kōyilolugu serves not only as a historical document but as the living authority for temple procedure — when disputes arise about the proper manner of worship, the kōyilolugu is the reference. It preserves the continuity of the āgama tradition in the specific context of each temple.