• Evaluates a given model or chain against a specified LangSmith dataset.

    This function fetches example records from the specified dataset, runs the model or chain against each example, and returns the evaluation results.


    • chainOrFactory: any

      A model or factory/constructor function to be evaluated. It can be a Runnable instance, a factory function that returns a Runnable, or a user-defined function or factory.

    • datasetName: string

      The name of the dataset against which the evaluation will be performed. This dataset should already be defined and contain the relevant data for evaluation.

    • Optional options: RunOnDatasetParams

      (Optional) Additional parameters for the evaluation process:

      • evaluators (RunEvalType[]): Evaluators to apply to a dataset run.
      • formatEvaluatorInputs (EvaluatorInputFormatter): Convert the evaluation data into formats that can be used by the evaluator.
      • projectName (string): Name of the project for logging and tracking.
      • projectMetadata (Record<string, unknown>): Additional metadata for the project.
      • client (Client): Client instance for LangSmith service interaction.
      • maxConcurrency (number): Maximum concurrency level for dataset processing.

    Returns Promise<EvalResults>

    A promise that resolves to an EvalResults object. This object includes detailed results of the evaluation, such as execution time, run IDs, and feedback for each entry in the dataset.


    // Example usage for evaluating a model on a dataset
    async function evaluateModel() {
    const chain = /* ...create your model or chain...*//
    const datasetName = 'example-dataset';
    const client = new Client(/* ...config... *//);

    const results = await runOnDataset(chain, datasetName, {
    evaluators: [/* ...evaluators... *//],

    console.log('Evaluation Results:', results);


    In this example, runOnDataset is used to evaluate a language model (or a chain of models) against a dataset named 'example-dataset'. The evaluation process is configured using RunOnDatasetParams["evaluators"], which can include both standard and custom evaluators. The Client instance is used to interact with LangChain services. The function returns the evaluation results, which can be logged or further processed as needed.

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