LLM-based descriptors use an external LLM for evaluation. You can:

Use built-in evaluators (with pre-written prompts), or
Run evals for custom criteria you configure.

Pre-requisites:

You know how to use descriptors to evaluate text data.

Imports

from evidently.future.datasets import Descriptor
from evidently.features.llm_judge import BinaryClassificationPromptTemplate
from evidently.future.descriptors import LLMEval, ToxicityLLMEval, ContextQualityLLMEval, DeclineLLMEval

To generate toy data and create a Dataset object:

import pandas as pd
from evidently.future.datasets import Dataset
from evidently.future.datasets import DataDefinition

data = [
    ["Why is the sky blue?", 
     "The sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light.", 
     "because air scatters blue light more"],
    ["How do airplanes stay in the air?", 
     "Airplanes stay in the air because their wings create lift by forcing air to move faster over the top of the wing than underneath, which creates lower pressure on top.", 
     "because wings create lift"],
    ["Why do we have seasons?", 
     "We have seasons because the Earth is tilted on its axis, which causes different parts of the Earth to receive more or less sunlight throughout the year.", 
     "because Earth is tilted"],
    ["How do magnets work?", 
     "Magnets work because they have a magnetic field that can attract or repel certain metals, like iron, due to the alignment of their atomic particles.", 
     "because of magnetic fields"],
    ["Why does the moon change shape?", 
     "The moon changes shape, or goes through phases, because we see different portions of its illuminated half as it orbits the Earth.", 
     "because it rotates"],
    ["What movie should I watch tonight?", 
     "A movie is a motion picture created to entertain, educate, or inform viewers through a combination of storytelling, visuals, and sound.", 
     "watch a movie that suits your mood"]
]

columns = ["question", "context", "response"]

df = pd.DataFrame(data, columns=columns)

eval_df = Dataset.from_pandas(
  pd.DataFrame(df),
  data_definition=DataDefinition())

Built-in LLM evals

Available descriptors. Check all available built-in LLM evals in the reference table.

There are built-in evaluators for popular criteria, like detecting toxicity or if the text contains a refusal. These built-in descriptors:

Default to binary classifiers.
Default to using gpt-4o-mini model from OpenAI.
Return a label, the reasoning for the decision, and an optional score.

OpenAI key. Add the token as the environment variable: see docs.

import os
os.environ["OPENAI_API_KEY"] 

Run a single-column eval. For example, to evaluate whether responsecontains any toxicity:

eval_df.add_descriptors(descriptors=[
    ToxicityLLMEval("response", alias="toxicity"),
])

View the results as usual:

eval_df.as_dataframe()

Example output:

Run a multi-column eval. Some evaluators naturally require two columns. For example, to evaluate Context Quality (“does it have enough information to answer the question?”), you must run this evaluation over your context column, and pass the question column as a parameter.

eval_df.add_descriptors(descriptors=[
    ContextQualityLLMEval("context", alias="good_context", question="question"),
])

Example output:

Parametrize evaluators. You can switch the output format from category to score (0 to 1) or exclude the reasoning to get only the label:

eval_df.add_descriptors(descriptors=[
    DeclineLLMEval("response", alias="refusal", include_reasoning=False),
    ToxicityLLMEval("response", alias="toxicity", include_category=False),
    PIILLMEval("response", alias="PII", include_score=True), 
])

Column names. The alias you set defines the column name with the category. If you enable the score result as well, it will get the “Alias score” name.

Change the LLM. To choose to use a different model for the evals.

eval_df.add_descriptors(descriptors=[
    ToxicityLLMEval("response", alias="toxicity", provider="openai", model="gpt-3.5-turbo"),
])

Custom LLM evals

You can also create a custom LLM evaluator using the provided templates:

Choose a template.
Specify the evaluation criteria (grading logic and names of categories)

Evidently will then generate the complete evaluation prompt to send to the selected LLM together with the evaluation data.

Evaluate a single column

Binary classification template. For example, to evaluate if the text is “concise”:

conciseness = BinaryClassificationPromptTemplate(
        criteria = """Conciseness refers to the quality of being brief and to the point, while still providing all necessary information.
            A concise response should:
            - Provide the necessary information without extra details or repetition.
            - Be brief yet comprehensive enough to address the query.
            - Use simple and direct language to convey the message effectively.
        """,
        target_category="concise",
        non_target_category="verbose",
        uncertainty="unknown",
        include_reasoning=True,
        pre_messages=[("system", "You are a judge which evaluates text.")],
        )      

You do not need to explicitly ask the LLM to classify your input into two classes, return reasoning, or format the output. This is already part of the Evidently template.

To apply this descriptor for your data, pass the template name to the LLMEval descriptor:

eval_df.add_descriptors(descriptors=[
    LLMEval("response", 
            template=conciseness, 
            provider = "openai", 
            model = "gpt-4o-mini", 
            alias="Conciseness"),
    ])

Publish results as usual:

eval_df.as_dataframe()

Another example. This template is very flexible. For instance, you can use to decide if the question is appropriate to the scope of your LLM application. A simplified prompt:

appropriate_scope = BinaryClassificationPromptTemplate(
        pre_messages=[("system", "You are a judge which evaluates questions sent to a student tutoring app.")],
        criteria = """An appropriate question is any educational query related to
        - academic subjects (e.g., math, science, history)
        - general world knowledge or skills
        An inappropriate question is any question that is:
        - unrelated to educational goals, such as personal preferences, pranks, or opinions
        - offensive or aimed to provoke a biased response.
        """,
        target_category="appropriate",
        non_target_category="inappropriate",
        uncertainty="unknown",
        include_reasoning=True,
        )

Apply the template:

eval_df.add_descriptors(descriptors=[
    LLMEval("question", 
            template=appropriate_scope, 
            provider = "openai", 
            model = "gpt-4o-mini", 
            alias="appropriate_q"),
    ])

Example output:

Evaluate multiple columns

A custom evaluator can also use multiple columns. To implement this, mention the second {column_name} inside your evaluation criteria.

Example. To evaluate if the response is faithful to the context:

hallucination = BinaryClassificationPromptTemplate(
        pre_messages=[("system", "You are a judge which evaluates correctness of responses by comparing them to the trusted information source.")],
        criteria = """An hallucinated response is any response that
        - Contradicts the information provided in the source.
        - Adds any new information not provided in the source.
        - Gives a response not based on the source, unless it's a refusal or a clarifying question.

        A faithful response is the response that
        - Correctly uses the information from the source, even if it only partially.
        - A response that declines to answer.
        - A response that asks a clarifying question.

        Source:
        =====
        {context}
        =====
        """,
        target_category="hallucinated",
        non_target_category="faithful",
        uncertainty="unknown",
        include_reasoning=True,
        )

You do not need to include the primary column name in the evaluation prompt, since it’s already part of the template. You choose this column when you apply the descriptor.

When applying the descriptor, include the second column using the additional_columns parameter:

eval_df.add_descriptors(descriptors=[
    LLMEval("response", 
            template=hallucination, 
            provider = "openai", 
            model = "gpt-4o-mini", 
            alias="hallucination", 
            additional_columns={"context": "context"}),
])

Get the results as usual:

eval_df.as_dataframe()

Example output:

Parameters

LLMEval

Parameter	Description	Options
`template`	Sets a specific template for evaluation.	`BinaryClassificationPromptTemplate`
`provider`	The provider of the LLM to be used for evaluation.	`openai`
`model`	Specifies the model used for evaluation	Any available provider model (e.g., `gpt-3.5-turbo`, `gpt-4`)
`additional_columns`	A dictionary of additional columns present in your dataset to include in the evaluation prompt. Use it to map the column name to the placeholder name you reference in the `criteria`. For example: `({"mycol": "question"}`.	Custom dictionary (optional)

BinaryClassificationPromptTemplate

Parameter	Description	Options
`criteria`	Free-form text defining evaluation criteria.	Custom string (required)
`target_category`	Name of the target category you want to detect (e.g., you care about its precision/recall more than the other). The choice of “target” category has no impact on the evaluation itself. However, it can be useful for later quality evaluations of your LLM judge.	Custom category (required)
`non_target_category`	Name of the non-target category.	Custom category (required)
`uncertainty`	Category to return when the provided information is not sufficient to make a clear determination.	`unknown` (Default), `target`, `non_target`
`include_reasoning`	Specifies whether to include the LLM-generated explanation of the result.	`True` (Default), `False`
`pre_messages`	List of system messages that set context or instructions before the evaluation task. Use it to explain the evaluator role (“you are an expert..”) or context (“your goal is to grade the work of an intern..”).	Custom string (optional)

OpenAIPrompting

There is an earlier implementation of this approach with OpenAIPrompting descriptor. See the documentation below.

OpenAIPrompting Descriptor

To import the Descriptor:

from evidently.descriptors import OpenAIPrompting

Define a prompt. This is a simplified example:

pii_prompt = """
Please identify whether the below text contains personally identifiable information, such as name, address, date of birth, or other.
Text: REPLACE 
Use the following categories for PII identification:
1 if text contains PII
0 if text does not contain PII
0 if the provided data is not sufficient to make a clear determination
Return only one category.
"""

The prompt has a REPLACE placeholder that will be filled with the texts you want to evaluate. Evidently will take the content of each row in the selected column, insert into the placeholder position in a prompt and pass it to the LLM for scoring.

To compute the score for the column response and get a summary Report:

openai_prompting = Dataset.from_pandas(
    pd.DataFrame(data),
    data_definition=data_definition,
    descriptors=[
        OpenAI("Answer", prompt=pii_prompt, prompt_replace_string="REPLACE", model="gpt-3.5-turbo-instruct", 
               feature_type="num", alias="PII for Answer (by gpt3.5)"),
        
    ]
)

View as usual:

openai_prompting.as_dataframe()

Descriptor parameters

prompt: str
- The text of the evaluation prompt that will be sent to the LLM.
- Include at least one placeholder string.
prompt_replace_string: str
- A placeholder string within the prompt that will be replaced by the evaluated text.
- The default string name is “REPLACE”.
feature_type: str
- The type of Descriptor the prompt will return.
- Available types: num (numerical) or cat (categorical).
- This affects the statistics and default visualizations.
context_replace_string: str
- An optional placeholder string within the prompt that will be replaced by the additional context.
- The default string name is “CONTEXT”.
context: Optional[str]
- Additional context that will be added to the evaluation prompt, which does not change between evaluations.
- Examples: a reference document, a set of positive and negative examples, etc.
- Pass this context as a string.
- You cannot use context and context_column simultaneously.
context_column: Optional[str]
- Additional context that will be added to the evaluation prompt, which is specific to each row.
- Examples: a chunk of text retrieved from reference documents for a specific query.
- Point to the column that contains the context.
- You cannot use context and context_column simultaneously.
model: str
- The name of the OpenAI model to be used for the LLM prompting, e.g., gpt-3.5-turbo-instruct.
openai_params: Optional[dict]
- A dictionary with additional parameters for the OpenAI API call.
- Examples: temperature, max tokens, etc.
- Use parameters that OpenAI API accepts for a specific model.
possible_values: Optional[List[str]]
- A list of possible values that the LLM can return.
- This helps validate the output from the LLM and ensure it matches the expected categories.
- If the validation does not pass, you will get None as a response label.
alias: Optional[str]
- A display name visible in Reports and as a column name in tabular export.
- Use it to name your Descriptor.

Reference

Metric Customization

Explainers

Custom LLM Judge

Imports

Built-in LLM evals

Custom LLM evals

Evaluate a single column

Evaluate multiple columns

Parameters

LLMEval

BinaryClassificationPromptTemplate

OpenAIPrompting

Descriptor parameters

Reference

Metric Customization

Explainers

​Imports

​Built-in LLM evals

​Custom LLM evals

​Evaluate a single column

​Evaluate multiple columns

​Parameters

​LLMEval

​BinaryClassificationPromptTemplate

OpenAIPrompting

Descriptor parameters

Imports

Built-in LLM evals

Custom LLM evals

Evaluate a single column

Evaluate multiple columns

Parameters

LLMEval

BinaryClassificationPromptTemplate