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LLM Comparator: Python Library

The LLM Comparator Python Library provides a simple API for configuring and running comparative evaluations of models, and generating the JSON files required to analyze these models side-by-side in the LLM Comparator app.

Installation

# [OPTIONAL] We recommend using a Python virtual environemnt.
python3 -m venv ~/.venv/llm_comparator
source ~/.venv/llm_comparator/bin/activate

You can install this library from the PyPI registry. This workflow is recommended for most usage.

pip install llm_comparator

Or by cloning the repo from GitHub and installing from source. This workflow is recommended for contributors fixing bugs or adding new features to the library.

git clone https://github.com/PAIR-code/llm-comparator.git
cd llm-comparator/python
pip install -e .

Core Concepts

The primary entrypoint to the LLM Comparator Python Library is the llm_comparator.comparison module. This module provides a run() function that coordinates the three phases of comparative evaluation: judging, bulletizing, and clustering. The library provides modules for each of these phases, as well as wrappers for interacting with LLMs.

Model Helpers

The llm_comparator.model_helper module is used to initialize API wrappers to interface with LLMs. Broadly, we support two kinds of models: generation models, which should be text-to-text language models, and embedding models.

We provide concrete two concrete implementations of wrappers that interact with the Google Vertex AI API:

  • VertexGenerationModelHelper supports any generative language model available in the Model Garden. By default we use gemini-pro, but alternatives can be configured with the model_name= constructor parameter.
  • VertexEmbeddingModelHelper supports any text embedding model available in the Model Garden. By default we use textembedding-gecko@003, but alternatives can be configured with the model_name= constructor parameter.

Additional wrapper classes can be implemented by subclassing GenerationModelHelper and EmbeddingModelHelper as necessary. We welcome contributions of these classes to the library via Pull Requests.

Judges

The "judge" is the model responsible for actually doing the comparison between the two model responses.

This functionality is encapsulated in the LLMJudgeRunner from the llm_comparator.llm_judge_runner module. It requires a generator model that conforms to the GenerationModelHelper protocol in order to call an LLM to generate their judgements of which of the two model responses is better for every prompt.

We provide a default judge prompt in llm_comparator.llm_judge_runner.DEFAULT_LLM_JUDGE_PROMPT_TEMPLATE, and you can use the llm_judge_prompt_template= parameter to provide a custom prompt that may better suit your needs at initialization time. Prompts should require the judge to phrase its responses in a simple XML format that includes the verdict and an explanation, to enable downstream processing by the buletizer and clusterer. Note that if you do provide a custom prompt, you can use the rating_to_score_map= parameter to ensure judgement verdicts can be mapped to numeric values.

<result>
  <explanation>YOUR EXPLANATION GOES HERE.</explanation>
  <verdict>A is slightly better</verdict>
</result>

The same judge is run multiple times during each comparative analysis to get a diversity of ratings. This can be configured via the num_repeats= key of the optional judge_opts= dictionary passed to llm_comparator.comparison.run(). By default, we call the judge 6 times.

Bulletizers

A "bulletizer" condenses the results provided by the judge into a set of bullets to make them easier to understand and consume in the UI.

This functionality is encapsulated in the RationaleBulletGenerator from the llm_comparator.rationale_bullet_generator module. It requires a generator model that conforms to the GenerationModelHelper protocol in order to call an LLM to generate the bulleted summaries.

The primary configuration is the win_rate_threshold= parameter, which can be configured per-comparative evaluation run via the bulletizer_opts= dictionary passed to llm_comparator.comparison.run(). By default, the threshold is set to 0.25 based on the default scoring range of [-1.5, 1.5].

Clusterers

A "clusterer" takes the bullets, embeds them, groups them into clusters based on embedding similarity, and generates a label for those clusters.

This functionality is encapsulated in the RationaleClusterGenerator from the llm_comparator.rationale_cluster_generator module. It requires a generator model that conforms to the GenerationModelHelper protocol and an embedder that conforms to the EmbeddingModelHelper protocol in order to call LLMs to generate the clustered summary of rationale bullets.

The primary configuration is the num_clusters= parameter, which can be configured per-comparative evaluation run via the clusterer_opts= dictionary passed to llm_comparator.comparison.run(). By default, a clusterer creates 8 clusters from the bullets.

Basic Usage

We have prepared a Python notebook that you can open in Google Colab to follow along interactively. It uses Google's Vertex AI APIs to call models, and requires you to authenticate in order to follow along.

The following pseudo-script is the minimal distillation of the notebook linked above, without any AI platform-specific guidance.

from llm_comparator import comparison
from llm_comparator import model_helper
from llm_comparator import llm_judge_runner
from llm_comparator import rationale_bullet_generator
from llm_comparator import rationale_cluster_generator

inputs = [
  # Provide your inputs here.
  # They must conform to llm_comparator.types.LLMJudgeInput
]

# Initialize the models-calling classes.
generator = # Initialize a model_helper.GenerationModelHelper() subclass
embedder = # Initialize a model_helper.EmbeddingModelHelper() subclass

# Initialize the instances that run work on the models.
judge = llm_judge_runner.LLMJudgeRunner(generator)
bulletizer = rationale_bullet_generator.RationaleBulletGenerator(generator)
clusterer = rationale_cluster_generator.RationaleClusterGenerator(
    generator, embedder
)

# Configure and run the comparative evaluation.
comparison_result = comparison.run(inputs, judge, bulletizer, clusterer)

# Write the results to a JSON file that can be loaded in
# https://pair-code.github.io/llm-comparator
file_path = "path/to/file.json"
comparison.write(comparison_result, file_path)