What problem does it solve? Measuring whether an LLM application actually works well is hard: manual spot-checks don't scale, regressions slip into production unnoticed, and comparing models or prompts lacks rigor. This Skill provides a complete evaluation toolkit covering automated metrics, human evaluation, LLM-as-judge patterns, and statistical A/B testing. ## Core Features & Use Cases - Automated Metrics: Implement BLEU, ROUGE, BERTScore, perplexity, and custom metrics like groundedness, toxicity, and factuality using NLI models. - LLM-as-Judge: Use Claude for pointwise scoring, pairwise comparison, and reference-based evaluation with structured Pydantic outputs. - Human Evaluation & A/B Testing: Build annotation frameworks with inter-rater agreement (Cohen's kappa) and run statistically rigorous A/B tests with t-tests and Cohen's d effect sizes. - Regression Detection & Benchmarking: Compare new results against baselines to catch performance regressions, and integrate with LangSmith for dataset-driven evaluation. - Use Case: Before deploying a prompt change to your RAG chatbot, run the evaluation suite against your test dataset, compare results to the baseline with the regression detector, and confirm the improvement is statistically significant via the A/B testing framework. ## Quick Start Ask the AI to set up an evaluation suite with accuracy, BERTScore, and a groundedness metric, then run it against your test cases and flag any regressions versus your baseline.