@mastra/langsmith

LangSmith AI Observability exporter for Mastra applications.

Installation

npm install @mastra/langsmith

Usage

Zero-Config Setup

The exporter automatically reads credentials from environment variables:

# Required
LANGSMITH_API_KEY=lsv2_pt_...

# Optional
LANGCHAIN_PROJECT=my-project  # Project name, defaults to "default"

import { LangSmithExporter } from '@mastra/langsmith';

const mastra = new Mastra({
  ...,
  observability: {
    configs: {
      langsmith: {
        serviceName: 'my-service',
        exporters: [new LangSmithExporter()],
      },
    },
  },
});

Explicit Configuration

You can also pass credentials directly:

import { LangSmithExporter } from '@mastra/langsmith';

const mastra = new Mastra({
  ...,
  observability: {
    configs: {
      langsmith: {
        serviceName: 'my-service',
        exporters: [
          new LangSmithExporter({
            apiKey: 'lsv2_pt_...',
            projectName: 'my-custom-project', // Optional
          }),
        ],
      },
    },
  },
});

Configuration Options

| Option | Type | Description | | ------------- | -------- | ------------------------------------------------------------------------------------------ | | apiKey | string | LangSmith API key. Defaults to LANGSMITH_API_KEY env var | | projectName | string | The name of the LangSmith project to send traces to. Overrides LANGCHAIN_PROJECT env var | | apiUrl | string | Custom LangSmith API URL (for self-hosted instances) | | client | Client | Custom LangSmith client instance |

Features

Tracing

• Automatic span mapping: Root spans become LangSmith traces
• Type-specific metadata: Extracts relevant metadata for each span type (agents, tools, workflows)
• Error tracking: Automatic error status and message tracking
• Hierarchical traces: Maintains parent-child relationships
• Event span support: Zero-duration spans for event-type traces