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The Line platform includes a suite of tools for evaluating how your Agent is performing, both during development phase and in production. You have full control over how metrics for evaluating your agent are defined.

Using Metrics

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System Metrics

By default, all calls made by a Line Agent have a set of system metrics automatically calculated to help evaluate performance.
System MetricDescription
system_call_successA boolean status indicating if the call disconnects unexpectedly, for example due to reasoning code crashing
system_text_to_speech_ttfbThe time to first byte of audio generated by the TTS model on the first turn of the conversation

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LLM as a Judge

An LLM-as-a-Judge metric is created in the playground by setting a name and specifying a prompt. You can try out different prompts in the playground against existing call transcripts by copying a call id into the metric creation field and clicking evaluate to generate a sample output.

Create a Custom Metric Demo

Write your LLM as a Judge metrics to return a single value and description field.
A metric name can only include lower case letters, digits, and ‘-’, ‘_’, or ‘.’ characters so that you can manage it from a cli. Metric names must also be unique within your organization.

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Assigning Metrics

Once a metric is created, it can be assigned to an Agent via the playground from the Agent page. All subsequent calls made to or from that Agent will have metric results calculated and available to view in the console and API. Note that when you assign a metric to an existing Agent, it won’t be automatically run on previous calls.
Assign a metric