Add LLM-as-a-Judge guide

[ankrgyl]

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Summary

This new cookbook example walks through how to create a custom LLM-as-a-judge, and in particular explores (a) different methods (numeric rating vs. classification) and (b) how to evaluate each method's effectiveness.

Motivation

Creating good LLM-as-a-judge scorers is an important challenge, and there's not a lot of content out there on how to do it. It's also important to eval and measure them just like you would any AI application, so hopefully this example can help folks understand how to do that.

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