Skip to main content

Model-graded metrics

promptfoo supports several types of model-graded assertions:

Output-based:

  • llm-rubric - checks if the LLM output matches given requirements, using a language model to grade the output based on the rubric.
  • model-graded-closedqa - similar to the above, a "criteria-checking" eval that ensures the answer meets a specific requirement. Uses an OpenAI-authored prompt from their public evals.
  • factuality - a factual consistency eval which, given a completion A and reference answer B evaluates whether A is a subset of B, A is a superset of B, A and B are equivalent, A and B disagree, or A and B differ, but difference don't matter from the perspective of factuality. Uses the prompt from OpenAI's public evals.
  • answer-relevance - ensure that LLM output is related to original query
  • classifier - see classifier grading docs.
  • select-best - compare outputs from multiple test cases and choose a winner

RAG-based (requires query and/or context vars):

  • context-recall - ensure that ground truth appears in context
  • context-relevance - ensure that context is relevant to original query
  • context-faithfulness - ensure that LLM output uses the context

Examples (output-based)

Example of llm-rubric and/or model-graded-closedqa:

assert:
- type: model-graded-closedqa # or llm-rubric
# Make sure the LLM output adheres to this criteria:
value: Is not apologetic

Example of factuality check:

assert:
- type: factuality
# Make sure the LLM output is consistent with this statement:
value: Sacramento is the capital of California

For more information on factuality, see the guide on LLM factuality.

Here's an example output that indicates PASS/FAIL based on LLM assessment (see example setup and outputs):

LLM prompt quality evaluation with PASS/FAIL expectations

Using variables in the rubric

You can use test vars in the LLM rubric. This example uses the question variable to help detect hallucinations:

providers: [openai:gpt-3.5-turbo]
prompts: [prompt1.txt, prompt2.txt]
defaultTest:
assert:
- type: llm-rubric
value: 'Says that it is uncertain or unable to answer the question: "{{question}}"'
tests:
- vars:
question: What's the weather in New York?
- vars:
question: Who won the latest football match between the Giants and 49ers?

Examples (RAG-based)

RAG metrics require variables named context and query. You must also set the threshold property on your test (all scores are normalized between 0 and 1).

Here's an example config of a RAG-based knowledge bot that evaluates RAG context metrics:

prompts:
- |
You are an internal corporate chatbot.
Respond to this query: {{query}}
Here is some context that you can use to write your response: {{context}}
providers: [openai:gpt-4]
tests:
- vars:
query: What is the max purchase that doesn't require approval?
context: file://docs/reimbursement.md
assert:
- type: contains
value: '$500'
- type: factuality
value: the employee's manager is responsible for approvals
- type: answer-relevance
threshold: 0.9
- type: context-recall
threshold: 0.9
value: max purchase price without approval is $500. Talk to Fred before submitting anything.
- type: context-relevance
threshold: 0.9
- type: context-faithfulness
threshold: 0.9
- vars:
query: How many weeks is maternity leave?
context: file://docs/maternity.md
assert:
- type: factuality
value: maternity leave is 4 months
- type: answer-relevance
threshold: 0.9
- type: context-recall
threshold: 0.9
value: The company offers 4 months of maternity leave, unless you are an elephant, in which case you get 22 months of maternity leave.
- type: context-relevance
threshold: 0.9
- type: context-faithfulness
threshold: 0.9

Examples (comparison)

The select-best assertion type is used to compare multiple outputs in the same TestCase row and select the one that best meets a specified criterion.

Here's an example of how to use select-best in a configuration file:

prompts:
- "Write a tweet about {{topic}}"
- "Write a very concise, funny tweet about {{topic}}"

providers: [openai:gpt-4]

tests:
- vars:
topic: bananas
assert:
- type: select-best
value: choose the funniest tweet

- vars:
topic: nyc
assert:
- type: select-best
value: choose the tweet that contains the most facts

Overriding the LLM grader

By default, model-graded asserts use GPT-4 for grading. If you do not have access to GPT-4 or prefer not to use it, you can override the rubric grader. There are several ways to do this, depending on your preferred workflow:

  1. Using the --grader CLI option:

    promptfoo eval --grader openai:gpt-3.5-turbo
  2. Using test.options or defaultTest.options on a per-test or testsuite basis:

    defaultTest:
    options:
    provider: openai:gpt-3.5-turbo
    tests:
    - description: Use LLM to evaluate output
    assert:
    - type: llm-rubric
    value: Is spoken like a pirate
  3. Using assertion.provider on a per-assertion basis:

    tests:
    - description: Use LLM to evaluate output
    assert:
    - type: llm-rubric
    value: Is spoken like a pirate
    provider: openai:gpt-3.5-turbo

Use the provider.config field to set custom parameters:

provider:
- id: openai:gpt-3.5-turbo
config:
temperature: 0

Also note that custom providers are supported as well.

Overriding the rubric prompt

For the greatest control over the output of llm-rubric, you may set a custom prompt using the rubricPrompt property of TestCase or Assertion.

The rubric prompt has two built-in variables that you may use:

  • {{output}} - The output of the LLM (you probably want to use this)
  • {{rubric}} - The value of the llm-rubric assert object

In this example, we set rubricPrompt under defaultTest, which applies it to every test in this test suite:

defaultTest:
options:
rubricPrompt:
- role: system
content: >-
Grade the output by the following specifications, keeping track of the points scored:

Did the output mention {{x}}? +1 point
Did the output describe {{y}}? + 1 point
Did the output ask to clarify {{z}}? +1 point

Calculate the score but always pass the test. Output your response in the following JSON format:
{pass: true, score: number, reason: string}
- role: user
content: 'Output: {{ output }}'

See the full example.

select-best rubric prompt

For control over the select-best rubric prompt, you may use the variables {{outputs}} (list of strings) and {{criteria}} (string). It expects the LLM output to contain the index of the winning output.

Classifers

Classifiers can be used to detect tone, bias, toxicity, helpfulness, and much more. See classifier documentation.

Other assertion types

For more info on assertions, see Test assertions.