Evaluating a RAG Chat App

This repo contains scripts and tools for evaluating a chat app that uses the RAG architecture. There are many parameters that affect the quality and style of answers generated by the chat app, such as the system prompt, search parameters, and GPT model parameters.

Whenever you are making changes to a RAG chat with the goal of improving the answers, you should evaluate the results. This repository offers tools to make it easier to run evaluations, plus examples of evaluations that we've run on our popular RAG chat solution.

📺 Watch a video overview of this repo

Table of contents:

• Cost estimation
• Setting up this project
• Deploying a GPT-4 model
• Generating ground truth data
• Running an evaluation
• Viewing the results
• Measuring app's ability to say "I don't know"

Cost estimation

There are several places where this project can incur costs:

Cost	Description	Estimated tokens used
Generating ground truth data	This is a one-time cost for generating the initial set of questions and answers, and involves pulling data down from your search index and sending it to the GPT model.	1000 tokens per question generated, which would be 200,000 tokens for the recommended 200 questions.
Running evaluations	Each time you run an evaluation, you may choose to use the GPT-based evaluators (groundedness, coherence, etc). For each GPT-evaluator used, you will incur costs for the tokens used by the GPT model.	1000 tokens per question per evaluator used, which would be 600,000 tokens for the default 200 questions and 3 evaluators.

For a full estimate of the costs for your region and model, see the Azure OpenAI pricing page or use the Azure OpenAI pricing calculator.

Setting up this project

If you open this project in a Dev Container or GitHub Codespaces, it will automatically set up the environment for you. If not, then follow these steps:

1. Install Python 3.10 or higher

2. Create a Python virtual environment.

3. Inside that virtual environment, install the project:

   python -m pip install -e .

Deploying a GPT-4 model

It's best to use a GPT-4 model for performing the evaluation, even if your chat app uses GPT-3.5 or another model. You can either use an Azure OpenAI instance or an openai.com instance.

Using a new Azure OpenAI instance

To use a new Azure OpenAI instance, you'll need to create a new instance and deploy the app to it. We've made that easy to deploy with the azd CLI tool.

1. Install the Azure Developer CLI

2. Run azd auth login to log in to your Azure account

3. Run azd up to deploy a new GPT-4 instance

4. Create a .env file based on .env.sample:

   cp .env.sample .env

5. Run this commands to get the required values for AZURE_OPENAI_EVAL_DEPLOYMENT and AZURE_OPENAI_SERVICE from your deployed resource group and paste those values into the .env file:

   azd env get-value AZURE_OPENAI_EVAL_DEPLOYMENT
   azd env get-value AZURE_OPENAI_SERVICE

Using an existing Azure OpenAI instance

If you already have an Azure OpenAI instance, you can use that instead of creating a new one.

1. Create .env file by copying .env.sample

2. Fill in the values for your instance:

   AZURE_OPENAI_EVAL_DEPLOYMENT="<deployment-name>"
   AZURE_OPENAI_ENDPOINT="https://<service-name>.openai.azure.com"

3. The scripts default to keyless access (via AzureDefaultCredential), but you can optionally use a key by setting AZURE_OPENAI_KEY in .env.

Using an openai.com instance

If you have an openai.com instance, you can use that instead of an Azure OpenAI instance.

1. Create .env file by copying .env.sample

2. Change OPENAI_HOST to "openai" and fill in the key for for your OpenAI account. If you do not have an organization, you can leave that blank.

   OPENAI_HOST="openai"
   OPENAICOM_KEY=""
   OPENAICOM_ORGANIZATION=""

Generating ground truth data

In order to evaluate new answers, they must be compared to "ground truth" answers: the ideal answer for a particular question. See example_input/qa.jsonl for an example of the format. We recommend at least 200 QA pairs if possible.

There are a few ways to get this data:

1. Manually curate a set of questions and answers that you consider to be ideal. This is the most accurate, but also the most time-consuming. Make sure your answers include citations in the expected format. This approach requires domain expertise in the data.
2. Use a generator script to generate a set of questions and answers, and use them directly. This is the fastest, but may also be the least accurate.
3. Use a generator script to generate a set of questions and answers, and then manually curate them, rewriting any answers that are subpar and adding missing citations. This is a good middle ground, and is what we recommend.

Additional tips for ground truth data generation

• Generate more QA pairs than you need, then prune them down manually based on quality and overlap. Remove low quality answers, and remove questions that are too similar to other questions.
• Be aware of the knowledge distribution in the document set, so you effectively sample questions across the knowledge space.
• Once your chat application is live, continually sample live user questions (within accordance to your privacy policy) to make sure you're representing the sorts of questions that users are asking.

Running an evaluation

We provide a script that loads in the current azd environment's variables, installs the requirements for the evaluation, and runs the evaluation against the local app. Run it like this:

python -m evaltools evaluate --config=example_config.json

The config.json should contain these fields as a minimum:

{
    "testdata_path": "example_input/qa.jsonl",
    "target_url": "http://localhost:50505/chat",
    "requested_metrics": ["groundedness", "relevance", "coherence", "latency", "answer_length"],
    "results_dir": "example_results/experiment<TIMESTAMP>"
}

Running against a local container

If you're running this evaluator in a container and your app is running in a container on the same system, use a URL like this for the target_url:

"target_url": "http://host.docker.internal:50505/chat"

Running against a deployed app

To run against a deployed endpoint, change the target_url to the chat endpoint of the deployed app:

"target_url": "https://app-backend-j25rgqsibtmlo.azurewebsites.net/chat"

Running on a subset of questions

It's common to run the evaluation on a subset of the questions, to get a quick sense of how the changes are affecting the answers. To do this, use the --numquestions parameter:

python -m evaltools evaluate --config=example_config.json --numquestions=2

Specifying the evaluate metrics

The evaluate command will use the metrics specified in the requested_metrics field of the config JSON. Some of those metrics are built-in to the evaluation SDK, and the rest are custom metrics that we've added.

Built-in metrics

These metrics are calculated by sending a call to the GPT model, asking it to provide a 1-5 rating, and storing that rating.

Important

The built-in metrics are only intended for use on evaluating English language answers, since they use English-language prompts internally. For non-English languages, you should use the custom prompt metrics instead.

• gpt_coherence measures how well the language model can produce output that flows smoothly, reads naturally, and resembles human-like language.
• gpt_relevance assesses the ability of answers to capture the key points of the context.
• gpt_groundedness assesses the correspondence between claims in an AI-generated answer and the source context, making sure that these claims are substantiated by the context.
• gpt_similarity measures the similarity between a source data (ground truth) sentence and the generated response by an AI model.
• gpt_fluency measures the grammatical proficiency of a generative AI's predicted answer.
• f1_score Measures the ratio of the number of shared words between the model generation and the ground truth answers.

Custom metrics

Prompt metrics

The following metrics are implemented very similar to the built-in metrics, but use a locally stored prompt. They're a great fit if you find that the built-in metrics are not working well for you or if you need to translate the prompt to another language.

• mycoherence: Measures how well the language model can produce output that flows smoothly, reads naturally, and resembles human-like language. Based on scripts/evaluate_metrics/prompts/coherence.prompty.
• myrelevance: Assesses the ability of answers to capture the key points of the context. Based on scripts/evaluate_metrics/prompts/relevance.prompty.
• mygroundedness: Assesses the correspondence between claims in an AI-generated answer and the source context, making sure that these claims are substantiated by the context. Based on scripts/evaluate_metrics/prompts/groundedness.prompty.

Code metrics

These metrics are calculated with some local code based on the results of the chat app, and do not require a call to the GPT model.

• latency: The time it takes for the chat app to generate an answer, in seconds.
• length: The length of the generated answer, in characters.
• has_citation: Whether the answer contains a correctly formatted citation to a source document, assuming citations are in square brackets.
• citation_match: Whether the answer contains at least all of the citations that were in the ground truth answer.

Sending additional parameters to the app

This repo assumes that your chat app is following the AI Chat Protocol, which means that all POST requests look like this:

{"messages": [{"content": "<Actual user question goes here>", "role": "user"}],
 "context": {...},
}

Any additional app parameters would be specified in the context of that JSON, such as temperature, search settings, prompt overrides, etc. To specify those parameters, add a target_parameters key to your config JSON. For example:

    "target_parameters": {
        "overrides": {
            "semantic_ranker": false,
            "prompt_template": "<READFILE>example_input/prompt_refined.txt"
        }
    }

The overrides key is the same as the overrides key in the context of the POST request. As a convenience, you can use the <READFILE> prefix to read in a file and use its contents as the value for the parameter. That way, you can store potential (long) prompts separately from the config JSON file.

Specifying the location of answer and context in response

The evaluator needs to know where to find the answer and context in the response from the chat app. If your app returns responses following the recommendations of the AI Chat Protocol, then the answer will be "message": "content" and the context will be a list of strings in "context": "data_points": "text".

If your app returns responses in a different format, you can specify the JMESPath expressions to extract the answer and context from the response. For example:

    "target_response_answer_jmespath": "message.content",
    "target_response_context_jmespath": "context.data_points.text"

Viewing the results

The results of each evaluation are stored in a results folder (defaulting to example_results). Inside each run's folder, you'll find:

• eval_results.jsonl: Each question and answer, along with the GPT metrics for each QA pair.
• parameters.json: The parameters used for the run, like the overrides.
• summary.json: The overall results, like the average GPT metrics.
• config.json: The original config used for the run. This is useful for reproducing the run.

To make it easier to view and compare results across runs, we've built a few tools, located inside the review-tools folder.

Using the summary tool

To view a summary across all the runs, use the summary command with the path to the results folder:

python -m evaltools summary example_results

This will display an interactive table with the results for each run, like this:

To see the parameters used for a particular run, select the folder name. A modal will appear with the parameters, including any prompt override.

Using the compare tool

To compare the answers generated for each question across 2 runs, use the compare command with 2 paths:

python -m evaltools diff example_results/baseline_1 example_results/baseline_2

This will display each question, one at a time, with the two generated answers in scrollable panes, and the GPT metrics below each answer.

]

Use the buttons at the bottom to navigate to the next question or quit the tool.

You can also filter to only show questions where the value changed for a particular metric, like this:

python -m evaltools diff example_results/baseline_1 example_results/baseline_2 --changed=has_citation

Measuring app's ability to say "I don't know"

The evaluation flow described above focused on evaluating a model’s answers for a set of questions that could be answered by the data. But what about all those questions that can’t be answered by the data? Does your model know how to say “I don’t know?” The GPT models are trained to try and be helpful, so their tendency is to always give some sort of answer, especially for answers that were in their training data. If you want to ensure your app can say “I don’t know” when it should, you need to evaluate it on a different set of questions with a different metric.

Generating ground truth data for answer-less questions

For this evaluation, our ground truth data needs to be a set of question whose answer should provoke an "I don’t know" response from the data. There are several categories of such questions:

• Unknowable: Questions that are related to the sources but not actually in them (and not public knowledge).
• Uncitable: Questions whose answers are well known to the LLM from its training data, but are not in the sources. There are two flavors of these:
  • Related: Similar topics to sources, so LLM will be particularly tempted to think the sources know.
  • Unrelated: Completely unrelated to sources, so LLM shouldn’t be as tempted to think the sources know.
• Nonsensical: Questions that are non-questions, that a human would scratch their head at and ask for clarification.

You can write these questions manually, but it’s also possible to generate them using a generator script in this repo, assuming you already have ground truth data with answerable questions.

python -m evaltools generate-dontknows --input=example_input/qa.jsonl --output=example_input/qa_dontknows.jsonl --numquestions=45

That script sends the current questions to the configured GPT-4 model along with prompts to generate questions of each kind.

When it’s done, you should review and curate the resulting ground truth data. Pay special attention to the "unknowable" questions at the top of the file, since you may decide that some of those are actually knowable, and you may want to reword or rewrite entirely.

Running an evaluation for answer-less questions

This repo contains a custom GPT metric called "dontknowness" that rates answers from 1-5, where 1 is "answered the question completely with no certainty" and 5 is "said it didn't know and attempted no answer". The goal is for all answers to be rated 4 or 5.

Here's an example configuration JSON that requests that metric, referencing the new ground truth data and a new output folder:

{
    "testdata_path": "example_input/qa_dontknows.jsonl",
    "results_dir": "example_results_dontknows/baseline",
    "requested_metrics": ["dontknowness", "answer_length", "latency", "has_citation"],
    "target_url": "http://localhost:50505/chat",
    "target_parameters": {
    },
    "target_response_answer_jmespath": "message.content",
    "target_response_context_jmespath": "context.data_points.text"
}

We recommend a separate output folder, as you'll likely want to make multiple runs and easily compare between those runs using the review tools.

Run the evaluation like this:

python -m evaltools evaluate --config=dontknows.config.json

The results will be stored in the results_dir folder, and can be reviewed using the review tools.

Improving the app's ability to say "I don't know"

If the app is not saying "I don't know" enough, you can use the diff tool to compare the answers for the "dontknows" questions across runs, and see if the answers are improving. Changes you can try:

• Adjust the prompt to encourage the model to say "I don't know" more often. Remove anything in the prompt that might be distracting or overly encouraging it to answer.
• Try using GPT-4 instead of GPT-3.5. The results will be slower (see the latency column) but it may be more likely to say "I don't know" when it should.
• Adjust the temperature of the model used by your app.
• Add an additional LLM step in your app after generating the answer, to have the LLM rate its own confidence that the answer is found in the sources. If the confidence is low, the app should say "I don't know".