What is istg in text?

ISTG stands for "I Swear to God." It is a slang term commonly used in online communication to emphasize the truthfulness or sincerity of a statement. When someone says "ISTG," they are essentially swearing on something they hold sacred or important to them, such as their faith or integrity. It is often used to express frustration, anger, or disbelief, and can convey a sense of intensity in the message being conveyed.