LLM-as-a-Judge: Complete Guide to Using LLMs as Evaluators

Wed, 23 Sep 2026 00:00:00 +0800

TL;DR

When an AI grades another AI’s answers, it needs instructions on what a good answer looks like and how many points each part earns. LLM-as-a-judge is the name for this setup (one AI doing the grading instead of a person), and it’s the only realistic way to check thousands of answers instead of a few dozen.
This only works if three things are true: the grading instructions actually catch the specific mistake they’re meant to catch, the AI grader isn’t quietly favouring one answer over another for reasons that have nothing to do with quality, and someone tested the grader on answers with a known correct score before trusting it on real ones.
There are two ways to use an AI grader: score one answer on its own, or show it two answers and ask which is better. These answer different questions, and using the wrong one for the job is a common mistake.

Key Takeaways

Evaluation on Eigenform Articles