Developer shares $4,200 lesson on Promptfoo's limits in LLM evaluation

A developer recounts a costly mistake where they treated Promptfoo as a comprehensive evaluation framework, leading to a $4,200 bill and production bugs. Promptfoo was found to be a regression test runner, not a true evaluator, as its automated judge had a low Cohen's kappa score of 0.47 when compared to human labels. The solution involved separating Promptfoo for CI gating and implementing a new pipeline to validate the judge against human-scored production traces, which improved the kappa score to 0.68. AI

IMPACT Highlights the critical need for robust evaluation beyond simple regression testing in LLM development to avoid costly production issues.

RANK_REASON Developer's personal account of a mistake and its resolution, not a new product release or industry-wide benchmark.

Read on dev.to — LLM tag →

• GPT-4
• LangSmith
• Promptfoo

• product
• other

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