Fine Tuning Metrics Definition

Does anyone have an idea of what loss function is used in the fine-tuning process, I have fine-tuned a 4o-mini model with 130 examples and I don’t find an exact documentation that defines the loss function. If I assume its cross-entropy loss, then I can interpret it by a negative exponential function, but how do I confirm this? I don’t want to assume that a full validation loss of 0.5317 is “good”, if I can get the function my interpretation would make sense. Thanks!