The Vira Agama is one of the twenty-eight Siddhāntāgamas, which is a classification of the Śaiva division of Śaivāgamas. The Śaivāgamas represent the wisdom that has come down from lord Śiva, received by Pārvatī and accepted by Viṣṇu.
According to the Kamika Agama, Vira means “neck portion”, and “The Vira Agama was revealed to Tejas as consisted of one hundred thousand verses. Prajapati received this Agama from Tejas. There are thirteen secondary Agamas for this Agama. They are: Prastara, Phullamalla, Prabodha, Bodha, Bodhaka, Amoha, Mohasamaya, Hakata, Sakatadhika, Hala, Vilekhana, Bhadra and Vira.”
According to this Wikipedia page, “The philosophy of Veerashaivism is explained in Siddhanta Shikhamani. While the Veerashaiva-tradition incorporates Vedic elements, the origin of panchacharyas has been explained in Sivagamas, especially in Svayambhuva Agama, Suprabhedagama and Viragama. The earlier portions of Agama literature are the fundamental source of Saiva religion, while the latter portions are of special importance to Veerashaivism”.