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promptfoo
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Promptfoo is an open-source CLI tool, co-founded by Ian Webster and Michael D'Angelo, for testing, evaluating, and red-teaming LLM applications, letting developers define test cases and run them against more than 50 model providers. Used by over 350,000 developers, the tool remains open source under the MIT license even after OpenAI announced its acquisition of the Promptfoo team in March 2026.
Tools
Promptfoo(github.com/promptfoo/promptfoo)
Promptfoo is an open-source tool for testing and evaluating LLM apps — declarative test cases, side-by-side model comparison, red-teaming, and CI/CD integration. Used by OpenAI and Anthropic.