LLM-as-a-Judge
When there's no reference answer and no rule to check, you can ask a strong model to grade the output — LLM-as-a-judge. It's the technique that made open-ended evaluation practical at scale, and it's also a minefield: judges have systematic biases, can be gamed, and agree with humans only when you design the grading carefully. Used well it's indispensable; used naively it produces confident numbers that mean nothing.
When there's no reference and no rule to check, you can ask a strong model to grade the output — LLM-as-a-judge. It made open-ended evaluation practical at scale, and it's a minefield: judges have systematic biases (position, verbosity, self-preference), can be gamed, and agree with humans only when you design the grading carefully.