The science of Haṭha should be kept completely secret by yogis who want success. It becomes potent when kept secret but impotent when revealed.
A critical edition and translation of the Haṭhapradīpikā, the most important premodern text on physical yoga, is available online:
Birch, Jason, James Mallinson, Jürgen Hanneder, Mitsuyo Demoto, and Nils Jacob Liersch. Haṭhapradīpikā Critical Edition and Translation. 2024. hathapradipika.online.