"No cap" means "no lie" or "I'm not lying." It's used to emphasize that what someone is saying is truthful or not exaggerated.
"No cap" directly stems from the slang use of "cap." By adding "no" in front of it, the phrase is used to assert that the statement being made is true and not a lie or exaggeration.
The phrase "no cap" became widely recognized and used in the mainstream, especially in music and social media, around the mid-2010s. It's often associated with hip-hop artists and their lyrics, where it was used to assert the truthfulness of their statements.
When you don't believe what the other person so you say no cap on jah. When saying this you invoke the god Jah and literally gain Jahseh Onfroy's knowledge and respect. You become one with X
Shank-Yo my cat just died
Person 2- No capon jah?
Shank- yeah.... rip jah 2k19