Prometheus-2 Cookbook - LlamaIndex
"An Open Source Language Model Specialized in Evaluating Other Language Models.".
About Prometheus-2 Cookbook - LlamaIndex
This page is a cookbook notebook from LlamaIndex's developer documentation. It shows how to use Prometheus 2, an open source language model that the page describes as specialized in evaluating other language models, as the judge for LlamaIndex's evaluators. The notebook covers pairwise comparison, faithfulness, correctness, and relevancy evaluation of retrieval-based question answering.
The demo depends on setup outside the model itself. Prometheus 2 must be deployed on Hugging Face Inference Endpoints or loaded locally, and the notebook uses OpenAI for building the index and for embeddings. The correctness evaluator requires labelled reference answers. The notebook uses a sample dataset of Paul Graham essays.
Key features
- Pairwise evaluator that compares responses from two query engines
- Faithfulness evaluator that checks whether answers stay within retrieved contexts
- Correctness evaluator that compares answers with labelled reference answers
- Relevancy evaluator that scores retrieved contexts and responses against a query
- Prometheus 2 used as the evaluation model through a Hugging Face endpoint
- Support for user-defined evaluation criteria in direct assessment and pairwise formats
Best for: Developers building retrieval-based question answering systems with LlamaIndex who want to evaluate outputs with an open judge model.
Good for
- Demonstrates four LlamaIndex evaluators in a single runnable notebook
- According to the paper abstract quoted on the page, Prometheus 2 supports both direct assessment and pairwise ranking
- The paper abstract reports closer agreement with human and GPT-4 judgements than earlier open evaluator models
Watch out for
- Prometheus 2 must be deployed on Hugging Face or loaded locally before the demo can run
- The demo uses OpenAI for index building and embeddings, which requires an OpenAI API key
- The correctness evaluator requires labelled reference answers
Prometheus-2 Cookbook - LlamaIndex at a glance
- Category
- Development › Developer Tools
- Type
- Website
- Pricing
- Not confirmed. Check the site
- Platforms
- Web
- Open source
- Not stated
- Language
- English
- Last checked
- Oct 6, 2026 · Online when checked
- Listed
- Oct 5, 2026
Guides for Developer Tools
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Prometheus-2 Cookbook - LlamaIndex FAQ
Does the demo require an OpenAI API key?
Yes. The notebook sets an OPENAI_API_KEY and uses OpenAI for the index and embedding model, while Prometheus 2 is used for evaluation.
How is Prometheus 2 hosted in the demo?
The notebook uses a model deployed on Hugging Face Inference Endpoints. The page notes that the model can also be loaded locally.
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