Structured test sets that measure the quality of an AI system's outputs in a repeatable, comparable way.
Evals are automated tests for the AI world. You prepare a list of real questions or tasks with expected answers or grading criteria, run the system on them and measure the results. Grading can be exact matching, rules, human review or another model judging the response.
Without evals it is hard to know whether a prompt change or a model switch improved things or made them worse. As models change and get updated, evals help you catch regressions before your customers notice them. Practical tip: start small: 20 to 30 real questions from your customers, including hard cases, different dialects and manipulation attempts. Run them after every significant change and keep the results so you can compare versions.