About GPTZero 

GPTZero is an AI detection, trained to detect ChatGPT, GPT4, BARD, Llama, and other AI models. Text prompts are reverse-engineered to test the AI's ability to recreate the input. GPTZero assesses text based on "perplexity" and "burstiness" by running it through a GPT-2 model. A lower perplexity score indicates a higher chance of artificial generation, while burstiness measures the occurrence of non-common items in human-written content.

https://gptzero.me