The distinction involving dharani and mantra is actually a tricky a single to create. We are able to say that all mantras are dharanis but that not all dharanis are mantras. Mantras do tend to be shorter. Both tend to comprise many unintelligible phonic fragments such as Om, or Hu.m https://edgartkbpg.blogolize.com/the-smart-trick-of-mantra-that-no-one-is-discussing-71771561