SelfCheckGPT is a zero-resource, black-box hallucination detection framework designed to evaluate the factuality of text generated by large language models without using external knowledge bases or internal model probabilities. The technique is based on the principle of self-consistency, generating multiple stochastic sample responses to the same prompt and evaluating them against the original text. Because a model that possesses reliable knowledge of a topic tends to produce consistent facts across independent samples, while false or hallucinated claims tend to diverge and contradict one another, the degree of consistency across the samples serves as a measure of factual reliability. This approach enables the identification of non-factual sentences and the assessment of passage-level factuality using only the generated outputs of the model.