This guide walks you through the process of evaluating your LLM application step-by-step. We assume that you are comfortable running experiments in Python or TypeScript and have an API key. If you haven’t already, make sure to read the evaluation quickstart first.

Experiment Comparison

Conceptualizing Testing & Evaluating LLM Applications

Because LLMs have non-deterministic behavior, it’s critical to understand the accuracy of your LLM app while you’re developing, and before you ship. It’s also important to track performance over time. It’s unlikely that you’ll ever hit 100% correctness, but it’s important that for the metrics you care about, you’re steadily improving. Parea’s experiments allow you to capture this into a simple, effective workflow that enables you ship more reliable, higher quality products.

To evaluate your LLM app, you need some data (10 samples are sufficient) and a function that executes a task. Your data need to contain the inputs to the function as key-value pairs and can optionally contain a ground truth value for that sample (indicated by the key target). While 10 samples are sufficient to get started, it’s useful to continue to add more samples whenever you identify new failure cases from your production traffic.

The goal of evaluation is to assess each of component and improve them over time. In practice, it’s better to assume for that your data is noisy, the LLM is imperfect, and evaluation methods are a little bit wrong.

Evaluation Metrics

You can either use pre-built SOTA evaluation metrics or define your own custom evaluation metrics. You can use evaluation metrics by attaching them via the trace decorator to your function. This will automatically execute the evaluation metric on the output of the function in non-blocking in the background after the function execution has finished. You can apply evaluations at any “level” of your application by attaching them to the corresponding function decorated with trace. This is useful to understand the quality at different levels of granularity (“Was the right context extracted?” vs. “Was the answer correct?”).

Using Pre-built SOTA Evaluations

Parea provides a set of state-of-the-art evaluation metrics you can plug into your evaluation process. Their motivation & research are discussed in the blog post on reference-free and reference-based evaluation metrics. Here is an overview of them:

Sometimes the exposed evaluation metrics are actually factory methods that return the evaluation metric. This is needed to configure the evaluation metric to your use case.

from parea import trace
from parea.evals.general import levenshtein

# annotate function with the trace decorator and pass the evaluation function(s)
def greeting(name: str) -> str:
    return f"Hello {name}"

# define the experiment and run it

Custom Evaluations

You can also define your own evaluation metrics. They can be as simple as checking if a certain word is in the output as shown below.

def eval_harmfulness(log: Log):
    return not "bad word" in log.output:

def experiment_entry_point(msg: str) -> str:
    return "good word"

To ensure that your evaluation metrics are reusable across the entire Parea ecosystem, and with any LLM models or LLM use cases, we introduced the log parameter. All evaluation functions accept the log parameter, which provides all the needed information to perform an evaluation. Evaluation functions are expected to return floating point scores or booleans.

Skipping Evaluation Metrics

Sometimes it’s useful to apply evaluation metrics only on a subset of the data. For that, you return None/null in the evaluation function to skip the evaluation for that log.

def my_eval_name(log: Log):
    if log.inputs.get("key") == "value-to-skip":
        return None
    return log.output ==

Return a Reason

While numerical scores are useful to get a fast grasp of how good a response is, it’s useful to provide a reason for why a response is bad. Especially, if one uses a LLM-based evaluation metric, it’s good to pass on the reasons for why the LLM assigned a certain score. You can do that by returning an EvaluationResult object with a reason attribute. Updating above example:

def eval_harmfulness(log: Log) -> EvaluationResult:
    if "bad word" in log.output:
        return EvaluationResult(name="harmfulness", score=0.0, reason="bad word found")
    return EvaluationResult(name="harmfulness", score=1.0)

def experiment_entry_point(msg: str) -> str:
    return "good word"

The full-definition of the EvaluationResult object is as follows:

Returning Multiple Scores

Sometimes there is shared work between different evaluation metrics such that returning multiple scores is better. You can do that by returning a list of EvaluationResult objects.

Running & Naming of Experiments

Depending on whether you use Python or TypeScript, you can name & run experiments in the below ways. You need to name an experiment and can optionally specify the name of a particular run. Note, that the run name can only contain alphanumeric characters, dashes, and underscores and needs to be unique within each project. After an experiment is finished, you will see an overview of the average stats and a link to the experiment page with full details.

In Python, you can define an experiment by calling the experiment method of the Parea client p and run it by calling the run method of the experiment. You can optionally specify the name of the run by passing it to the run method.

    name=experiment_name, # name of the experiment
    data=data,  # test data to run the experiment on (list of dicts)
    func=func,  # function to run (callable)
).run()         # you can optionally specify the run name by passing `run_name` to the run method

Alternatively, you can also use the CLI to run an experiment:

parea experiment path/to/

In this case the experiment file should contain the experiment definition but not call the run method. You can optionally specify the run name of the experiment using the --run_name flag in the CLI.

    name=experiment_name, # name of the experiment
    data=data,  # test data to run the experiment on (list of dicts)
    func=func,  # function to run (callable)

Within projects, you can organize your experiments by the experiment name. You can filter the experiments table by the experiment name to see all runs of that experiment. This will also filter the graph of historical experiment eval scores by that name.

Experiment Results by Experiment Names

Organize Experiments by Projects

You can organize your experiments by projects. By default, all logs, traces & experiments are grouped in the default project. You can specify a project name when you initialize the Parea client. This will automatically create a new project with that name if it didn’t exist before. Note, that the name of the project is only allowed to contain alphanumeric characters, dashes and underscores.

from parea import Parea

p = Parea(api_key=os.getenv("PAREA_API_KEY"), project_name='my-project')

You can toggle between projects on the platform by clicking on the project name in the collapsible sidebar on the left.

Testing Sub-steps

When building RAG applications, it’s useful to test the retrieval and generation steps separately to pinpoint what goes wrong. Similarly, when building agents, one typically wants to test every individual step for the expected output to catch cascading failures.

You can test sub-steps via Parea by attaching the trace decorator to the respective functions with the corresponding eval. This will create scores from every sub-step, when running the entrypoint function (no matter if running an experiment or running the function directly). To access different targets/expected outputs for sub-steps, you can pass the target as a dictionary when defining the experiment. Note, that this will convert the target to a string such that you will need to convert it back to a dictionary in the evaluation function in order to access the sub-step target. See Python & TypeScript examples below.


Given the non-deterministic behavior of LLMs it could be useful to run the evaluation multiple times per input to check response consistency, i.e., to run multiple trials. You can do that by specifying the n_trials parameter when defining an experiment:


Debug Individual Traces

You can debug individual traces to understand how your LLM app returned an output on specific inputs. You do that by clicking on the row in the log table of the experiment. In the trace view, you can step through the trace (left sidebar), see any inputs, outputs, and metadata (middle) of the selected step, and view any metrics and scores (right side).

Debug Trace

Use Saved Datasets

When running and experiment, you can use your datasets saved on Parea. For the data field just provide the name of the dataset as defined on the Datasets tab. The dataset should have column names that match the input parameters of the function you are running the experiment on. Note, the dataset name will be automatically stored in the “Dataset” key for the experiment metadata.

    name='Experiment Name',
    data="Dataset Name",

Dataset Level Evaluation

Sometimes it’s useful to aggregate the evaluation scores over the entire dataset, e.g., for balanced accuracy. You can do that by specifying the dataset_level_evals or datasetLevelEvals parameter when defining an experiment:

    dataset_level_evals=[...],  # list of evaluation functions applied on the entire dataset

The evaluation functions will receive a list of EvaluatedLog objects and are expected to return a single floating point score or a boolean. The EvaluatedLog object is a subclass of the Log object with the additional scores attribute. The scores will be attached to the Experiment and can be viewed in the overview table and the detailed view of the experiment.

Investigating Relationship Between Statistics

Sometimes it is useful to understand the relationship between different evaluation metrics, and, manual annotations. An example would be to assess how well your eval correlations / agrees with manual annotations. You can view a scatter plot of the relationship between two stats by selecting “Relationship between scores” in the dropdown above the graph in the detailed experiment view. Additionally, you can view the accuracy & correlation between the two selected variables and add that value to the experiment scores. Going back to the example of assessing how much your eval agrees with manual annotations, you can now track the quality of your eval over time and align it better with manual annotations.

Investigate Relationship

Sharing Experiments Publicly

All your experiments are shared by default in your organization and not publicly accessible. You can share experiments publicly by clicking on the Share button on the top right of the experiment page. This will generate a link following the format<org_slug>/<project_name>/<experiment_uuid> which anyone can access. You can compare all public experiments in a project under<org_slug>/<project_name>.

Visible Experiment

Experiment Code Management

As you iterate on your LLM app and test the changes, keeping track of which change led to which result is cumbersome. For that Parea provides an integration with DVC’s experiment tracking. This enables you to iterate on your LLM app without polluting your git history with a commit for every experiment and still have the ability to revert your code to the state of any experiment. Once integrated, every time you run an experiment, the state of the workspace together with the associated metrics will be automatically captured. This will enable you to compare experiment metrics and to revert your workspace to the state of them.

This is currently only supported for Python. Please, reach out if you want that functionality for TypeScript.

After integrating Parea with DVC, every time you run an experiment, Parea will capture the state of the workspace together with the associated metrics. To compare all ran experiments since the last commit you can run the following command and get below output:

dvc exp show

dvc exp show

To revert the code to the state of an experiment run the following using the run name of the experiment:

dvc exp apply <run-name>

You can learn more about dvc exp show here, and dvc exp apply here.

Add Metadata to Experiments

When running an experiment, you can add metadata to the experiment by passing a dictionary. These metadata will be displayed on the experiment overview table and can be used to filter and search for experiments.

    metadata={"Dataset": "Hello World Test"},

Experiment Metadata

Comparing Experiments

You can select 2 or more experiments in the experiment overview section and click on the Compare button to compare them. This will open up a new view which shows a high-level comparison of the experiment scores at the top and a side-by-side view of the individual results of the experiments on the same samples at the bottom.

The high-level comparison consists of 2-3 cards. The first card is only shown if 2 experiments are compared, and it displays for every evaluation metric how average and standard deviation have changed as well as the number of improvements and regressions. The second card compares the evaluation metric averages for every experiment as a bar plot. The third card shows the distribution plot of the selected evaluation metric as a histogram.

Experiment Comparison

Controlling Parallelism

You can specify on how many samples your experiment should be executed in parallel by setting the n_workers / nWorkers parameter when defining an experiment.


Integrate into CI/CD

After creating an experiment and evaluating your LLM app, you can integrate the experiment into your CI/CD pipeline as a test.

e = p.experiment(
assert all(score > 0.5 for score in e.avg_scores.values()), "Some scores are below 0.5"

Running Experiments in Jupyter Notebooks

In order to execute experiments in a Jupyter notebook, you will need to install nest-asyncio and apply it:

!pip install nest-asyncio
import nest_asyncio