Assess
Promptfoo is an open-source (MIT) tool for LLM evaluation and red teaming, built CLI-first: evals are declared in YAML configs (assertions, LLM-as-judge, RAG checks) and run locally or in CI with diff views and a GitHub Action.
Its standout capability is red teaming: 50+ attack plugins with presets for the OWASP LLM Top 10 - functional evaluation and LLM security testing in one tool
OpenAI acquired Promptfoo in March 2026. The tool remains MIT-licensed by commitment.