Most of the mantras are a A part of a Stotra or an Upanishad or maybe a fullfleged Sadhana or an Anushthana and had been hardly ever intended to be used in isolation. Even so, around a time period, several of the Pundits begun compiling the mantras and formulated books https://usanetdirectory.com/listings13303130/not-known-facts-about-world-famous-tantrik