Custom metrics. Eval Engineering for AI Developers, lesson 4 - learn how to write custom AI metrics

Galileo
363 views January 21, 2026

Learn Eval Engineering in this free, 5-part, hands-on course presented by @jimbobbennett ​90% of AI agents don't make it successfully to production. The biggest reason is the AI engineers building these apps don't have a clear way of evaluating that these agents are doing what they should do, and using the results of this evaluation to fix them. ​In this course, you will learn all about evals for AI applications. You'll start with some out-of-the-box metrics and learn about evals, then move onto understanding observability for AI apps, analyzing failure states, defining custom metrics, then finally using these across your whole SDLC. ​This will be hands on, so be prepared to write some code, create some metrics, and do some homework! ​In this fourth lesson, you will - Build datasets of known inputs and outputs for cases that pass and fail - Learn how to build custom metrics for your failure cases - Determine the success of your metrics by measuring true and false positives and negatives ​ Prerequisites: - ​A basic knowledge of Python ​- Access to an OpenAI API key - ​A free Galileo account (we will be using Galileo as the evals platform). Sign up at https://galileo.ai/sign-up. - Course materials from https://github.com/rungalileo/eval-engineering Catch the rest of the lessons here: https://youtube.com/playlist?list=PLS7keRo8770OODJn9HAEN8JKbIzTHME60 0:00:31 - Introduction & Overview 0:11:55 - Evaluation Driven Development: Moving Beyond Bug Fixes 0:16:45 - Data Strategy: Training, Dev, and Test Sets 0:27:07 - Creating Datasets from Trace Logs 0:32:12 - Anatomy of a Metric Prompt: Role, Criteria, Rubric & Examples 0:44:19 - Demo: Building a Custom Metric in Galileo 0:51:28 - Testing the Metric with Dev Data (Experiments) 1:01:42 - Iterating and Refining the Metric Prompt 1:08:24 - Scoring Your Metric: True Positive (TPR) & True Negative Rates (TNR) 1:23:44 - Homework: Using Metrics to Fix the App

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