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LangSmith Exporter

LangSmith is LangChain's platform for monitoring and evaluating LLM applications. The LangSmith exporter sends your AI traces to LangSmith, providing insights into model performance, debugging capabilities, and evaluation workflows.

When to Use LangSmithDirect link to When to Use LangSmith

LangSmith is ideal when you need:

  • LangChain ecosystem integration - Native support for LangChain applications
  • Debugging and testing - Detailed trace visualization and replay
  • Evaluation pipelines - Built-in evaluation and dataset management
  • Prompt versioning - Track and compare prompt variations
  • Collaboration features - Team workspaces and shared projects

InstallationDirect link to Installation

npm install @mastra/langsmith

ConfigurationDirect link to Configuration

PrerequisitesDirect link to Prerequisites

  1. LangSmith Account: Sign up at smith.langchain.com
  2. API Key: Generate an API key in LangSmith Settings → API Keys
  3. Environment Variables: Set your credentials
.env
LANGSMITH_API_KEY=ls-xxxxxxxxxxxx
LANGSMITH_BASE_URL=https://api.smith.langchain.com  # Optional for self-hosted

Basic SetupDirect link to Basic Setup

src/mastra/index.ts
import { Mastra } from "@mastra/core";
import { LangSmithExporter } from "@mastra/langsmith";

export const mastra = new Mastra({
  observability: {
    configs: {
      langsmith: {
        serviceName: "my-service",
        exporters: [
          new LangSmithExporter({
            apiKey: process.env.LANGSMITH_API_KEY,
          }),
        ],
      },
    },
  },
});

Configuration OptionsDirect link to Configuration Options

Complete ConfigurationDirect link to Complete Configuration

new LangSmithExporter({
  // Required credentials
  apiKey: process.env.LANGSMITH_API_KEY!,

  // Optional settings
  apiUrl: process.env.LANGSMITH_BASE_URL, // Default: https://api.smith.langchain.com
  callerOptions: {
    // HTTP client options
    timeout: 30000, // Request timeout in ms
    maxRetries: 3, // Retry attempts
  },
  logLevel: "info", // Diagnostic logging: debug | info | warn | error

  // LangSmith-specific options
  hideInputs: false, // Hide input data in UI
  hideOutputs: false, // Hide output data in UI
});