What is prompt evaluation? How to test prompts with metrics and judges

Prompt evaluation is a systematic approach for assessing the quality of AI model prompts by measuring their performance against structured test data across dimensions such as correctness, relevance, and safety. This method enables teams to objectively evaluate prompt changes using automated scoring and LLM-as-a-judge tools, which analyze outputs based on meaning and intent rather than surface text. The process emphasizes evidence-based assessments over subjective judgment, ensuring that prompt modifications yield real improvements before deployment. Prompt evaluation differs from prompt engineering by focusing on measuring the impact of prompt modifications against defined quality criteria. Tools like Braintrust facilitate end-to-end prompt evaluation by providing infrastructure for building golden datasets, employing built-in and custom scorers, and integrating evaluations into CI/CD workflows. This approach allows production teams to maintain prompt quality through automated regression testing and continuous monitoring, ultimately supporting faster iteration and more reliable AI feature deployment.