Testing AI prompts and comparing models with promptfoo

This article explains the importance of systematic testing for AI prompts as they become integral to applications. It introduces promptfoo, an open-source tool that automates prompt evaluation by running prompts and inputs against AI models, using predefined assertions to verify output quality. The tool helps catch regressions from prompt or model changes, supports comparing multiple models across vendors for quality, token usage, and cost, and covers deterministic and model-graded assertions. It is a practical guide for developers seeking to maintain prompt reliability and switch models without sacrificing performance.