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The faithfulness metric measures the quality of your RAG pipeline's generator by evaluating whether the actual_output factually aligns with the contents of your retrieval_context. deepeval's faithfulness metric is a self-explaining LLM-Eval, meaning it outputs a reason for its metric score.


Although similar to the HallucinationMetric, the faithfulness metric in deepeval is more concerned with contradictions between the actual_output and retrieval_context in RAG pipelines, rather than hallucination in the actual LLM itself.

Required Arguments

To use the FaithfulnessMetric, you'll have to provide the following arguments when creating an LLMTestCase:

  • input
  • actual_output
  • retrieval_context


from deepeval import evaluate
from deepeval.metrics import FaithfulnessMetric
from deepeval.test_case import LLMTestCase

# Replace this with the actual output from your LLM application
actual_output = "We offer a 30-day full refund at no extra cost."

# Replace this with the actual retrieved context from your RAG pipeline
retrieval_context = ["All customers are eligible for a 30 day full refund at no extra cost."]

metric = FaithfulnessMetric(
test_case = LLMTestCase(
input="What if these shoes don't fit?",


# or evaluate test cases in bulk
evaluate([test_case], [metric])

There are six optional parameters when creating a FaithfulnessMetric:

  • [Optional] threshold: a float representing the minimum passing threshold, defaulted to 0.5.
  • [Optional] model: a string specifying which of OpenAI's GPT models to use, OR any custom LLM model of type DeepEvalBaseLLM. Defaulted to 'gpt-4o'.
  • [Optional] include_reason: a boolean which when set to True, will include a reason for its evaluation score. Defaulted to True.
  • [Optional] strict_mode: a boolean which when set to True, enforces a binary metric score: 1 for perfection, 0 otherwise. It also overrides the current threshold and sets it to 1. Defaulted to False.
  • [Optional] async_mode: a boolean which when set to True, enables concurrent execution within the measure() method. Defaulted to True.
  • [Optional] verbose_mode: a boolean which when set to True, prints the intermediate steps used to calculate said metric to the console, as outlined in the How Is It Calculated section. Defaulted to False.

How Is It Calculated?

The FaithfulnessMetric score is calculated according to the following equation:

Faithfulness=Number of Truthful ClaimsTotal Number of Claims\text{Faithfulness} = \frac{\text{Number of Truthful Claims}}{\text{Total Number of Claims}}

The FaithfulnessMetric first uses an LLM to extract all claims made in the actual_output, before using the same LLM to classify whether each claim is truthful based on the facts presented in the retrieval_context.

A claim is considered truthful if it does not contradict any facts presented in the retrieval_context.