@mastra/langsmith

LangSmith AI Observability exporter for Mastra applications.

Installation

bash

npm install @mastra/langsmith

Usage

Zero-Config Setup

The exporter automatically reads credentials from environment variables:

bash

# Required
LANGSMITH_API_KEY=lsv2_pt_...

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

typescript

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:

typescript

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