Vajrasattva, the 'diamond being', is the Buddha of purification: white, a vajra held at the heart and a bell at the hip, seated on a moon disc, and in Tibetan practice the figure in whom the vajra lineage's transmission is concentrated — often counted as a sixth Tathagata completing the five-Buddha mandala. His hundred-syllable mantra, transmitted through the Yoga-tantra and Anuttarayoga cycles, is the standard means of confessing and purifying a broken vow, and the short form om vajrasattva hum is used across the schools. The four powers the practice requires — regret, reliance on the deity, the remedy of recitation, and the resolve not to repeat — are the tradition's own analysis of what confession is.
Modern Practice
He is the core of the ngondro: 100,000 recitations of the hundred-syllable mantra with the visualisation of white nectar purifying body, speech and mind, done before tantric practice proper. Modern practitioners also take him on retreat and after conflict, and the practice is the closest Tibetan Buddhism comes to a formal confession.