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Let your agent set this up. Copy the evaluations prompt into your coding agent to get started automatically.
An evaluation runs an evaluator on an input and an output and returns a verdict: a pass or fail, a score, a label, and the details behind it. LangWatch runs the same evaluators in three places: on a dataset in the Experiments Workbench, on production traces as an online evaluation, and inside your request as a guardrail.

Where evaluations run

Experiments

Online Evaluation

Guardrails

Evaluators

Which one to use

Start

Open Experiments, click New Experiment, add a dataset, a prompt and an evaluator, then click Run. See Experiments.
To score production traffic, open Online Evaluations, click New Online Evaluation, pick an evaluator, set the trace filter and the sampling rate, and save. See Setting up monitors. To block a response, call the evaluator from your code with as_guardrail=True and check passed before you answer the user:
See Guardrails for the TypeScript call and the error handling.

Datasets

Annotations

Last modified on September 8, 2026