AI Glossary Term

What does “LLM-as-Judge” mean?

Definition

Using a language model to score or compare outputs from other models during evaluation.

How LLM-as-Judge works

Diagram for LLM-as-Judge, steps in order: Two or more answers to grade; then Judge model gets a rubric; then Scores or picks the better one; then Aggregate across many cases.Two or more answers to gradeJudge model gets a rubricScores or picks the better oneAggregate across many cases

Example

To compare two summaries, a judge model is given the source text and a rubric on accuracy and clarity, then picks the better summary. A sample of its verdicts is checked by people.

Why it matters

It scales evaluation far beyond what people can review. Judges have biases, such as preferring longer answers, so they need calibration against human ratings.

Common questions

Can I trust it?

Reasonably for many tasks when checked against human judgments, but not blindly.

Known biases?

Preferences for longer answers, for the first option shown, and for its own style.

How to reduce bias?

Swap answer order, use clear rubrics, and compare against a human-labeled sample.

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