Langfuse JS/TS SDKs
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    Interface Evaluator

    One evaluator that can be used for scoring.

    An evaluator describes how to score data:

    • prompt
    • extracted prompt variables
    • output schema
    • optional explicit model configuration

    It does not define which live objects are evaluated. That is the job of evaluation-rules.

    For agent clients, the most important fields are:

    • variables: use these exact names when building the evaluation-rule mapping array
    • outputDefinition: tells you the expected score type and the evaluator's response instructions
    • modelConfig: tells you whether the evaluator uses the project default model (null) or an explicit provider/model

    Versioning behavior:

    • GET /evaluators returns the latest version of each available evaluator.
    • GET /evaluators/{id} can return an older version.
    • Evaluation rules always run against the latest version for the selected evaluator name within the same source (project or managed).
    interface Evaluator {
        createdAt: string;
        evaluationRuleCount: number;
        id: string;
        modelConfig: null | unstable.EvaluatorModelConfig;
        name: string;
        outputDefinition: unstable.PublicEvaluatorOutputDefinition;
        prompt: string;
        scope: unstable.EvaluatorScope;
        type: "llm_as_judge";
        updatedAt: string;
        variables: string[];
        version: number;
    }
    Index

    Properties

    createdAt evaluationRuleCount id modelConfig name outputDefinition prompt scope type updatedAt variables version

    Properties

    createdAt: string

    Timestamp when this evaluator was created.

    evaluationRuleCount: number

    Number of evaluation rules in the project that currently use this evaluator version.

    id: string

    Identifier of this evaluator.

    modelConfig: null | unstable.EvaluatorModelConfig

    Explicit model configuration, or null when the project default evaluation model is used.

    name: string

    Evaluator name.

    outputDefinition: unstable.PublicEvaluatorOutputDefinition

    Structured output schema returned by this evaluator.

    Responses always include dataType and omit the internal output-definition version. Use dataType to decide how future scores should be interpreted.

    prompt: string

    Prompt template used during evaluation.

    scope: unstable.EvaluatorScope

    Where this evaluator comes from: your project or Langfuse-managed defaults.

    type: "llm_as_judge"

    Evaluator engine type. Currently always llm_as_judge.

    updatedAt: string

    Timestamp when this evaluator was last updated.

    variables: string[]

    Variables extracted from the evaluator prompt.

    Every variable in this list must be mapped exactly once when creating an evaluation rule.

    version: number

    Version number of this evaluator.

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