LangSmithExporter

Sends Tracing data to LangSmith for observability.

Constructor

new LangSmithExporter(config: LangSmithExporterConfig)

LangSmithExporterConfig

interface LangSmithExporterConfig extends ClientConfig, BaseExporterConfig {
  client?: Client
  projectName?: string
}

Extends both ClientConfig (from LangSmith SDK) and BaseExporterConfig:

• From BaseExporterConfig: logger?: IMastraLogger, logLevel?: LogLevel | 'debug' | 'info' | 'warn' | 'error'
• From ClientConfig: apiKey, apiUrl, callerOptions, hideInputs, hideOutputs, etc.

Methods

exportTracingEvent

async exportTracingEvent(event: TracingEvent): Promise<void>

Exports a tracing event to LangSmith.

flush

async flush(): Promise<void>

Force flushes any pending spans to LangSmith without shutting down the exporter. Useful in serverless environments where you need to ensure spans are exported before the runtime terminates.

Waits for the LangSmith client's queued and in-flight batches. When the client uses manualFlushMode: true, this calls client.flush() for you, so you don't need to flush the client yourself. Overlapping calls wait for the earlier upload to finish.

shutdown

async shutdown(): Promise<void>

Ends all active spans and clears the trace map. Spans that are still open are ended with a shutdown error, and their updates are sent to LangSmith before the promise resolves.

Usage

import { LangSmithExporter } from '@mastra/langsmith'

const exporter = new LangSmithExporter({
  apiKey: process.env.LANGSMITH_API_KEY,
  projectName: 'my-project', // Optional: specify which project to send traces to
  apiUrl: 'https://api.smith.langchain.com',
  logLevel: 'info',
})

Environment variables

Variable	Description
LANGSMITH_API_KEY	Your LangSmith API key
LANGCHAIN_PROJECT	Default project name for traces (used if projectName not specified)
LANGSMITH_BASE_URL	API URL for self-hosted instances

Span type mapping

Span Type	LangSmith Type
MODEL_GENERATION	llm
MODEL_CHUNK	llm
TOOL_CALL	tool
MCP_TOOL_CALL	tool
PROVIDER_TOOL_CALL	tool
All others	chain

withLangsmithMetadata

Helper function to add LangSmith-specific metadata to tracing options.

function withLangsmithMetadata(metadata: LangSmithMetadataInput): TracingOptionsUpdater

LangSmithMetadataInput

Usage

import { buildTracingOptions } from '@mastra/observability'
import { withLangsmithMetadata } from '@mastra/langsmith'

// Route to a specific project
const tracingOptions = buildTracingOptions(withLangsmithMetadata({ projectName: 'my-project' }))

// Set multiple fields
const tracingOptions = buildTracingOptions(
  withLangsmithMetadata({
    projectName: 'my-project',
    sessionId: 'user-123',
  }),
)