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LangSmith Exporter

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

Installation​

npm install @mastra/langsmith@beta

Configuration​

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 Setup​

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

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

Configuration Options​

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
});