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README.md	README.md
package.json	package.json
tsconfig.json	tsconfig.json
tsup.config.ts	tsup.config.ts
typedoc.config.cjs	typedoc.config.cjs

@langfuse/otel

Langfuse is the open-source LLM engineering platform: tracing & evaluation for LLM and agent applications, prompt management, datasets & experiments, and evaluation (scores). This package provides the LangfuseSpanProcessor — the OpenTelemetry span processor that exports spans to Langfuse with smart filtering, masking, and media upload. Register it with any OTel setup and spans from @langfuse/tracing, the Vercel AI SDK, or any other GenAI instrumentation are sent to Langfuse. Prompt management, datasets/experiments, and evals/scores live in @langfuse/client.

Important

This is the current SDK generation (@langfuse/* scoped packages). The unscoped langfuse npm package is the legacy v3 SDK — for new integrations use @langfuse/tracing + @langfuse/otel. Migration guides: v3 → v4, v4 → v5.

Install

npm install @langfuse/otel @opentelemetry/sdk-trace-node

Environment variables

LANGFUSE_PUBLIC_KEY="pk-lf-..."
LANGFUSE_SECRET_KEY="sk-lf-..."
LANGFUSE_BASE_URL="https://cloud.langfuse.com" # 🇪🇺 EU region. 🇺🇸 US: https://us.cloud.langfuse.com

Quickstart

import { LangfuseSpanProcessor } from "@langfuse/otel";
import { NodeTracerProvider } from "@opentelemetry/sdk-trace-node";

export const langfuseSpanProcessor = new LangfuseSpanProcessor();

const tracerProvider = new NodeTracerProvider({
  spanProcessors: [langfuseSpanProcessor],
});

tracerProvider.register();

By default the processor exports Langfuse SDK spans, spans with gen_ai.*/ai.* attributes, and spans from known LLM instrumentation libraries — pass shouldExportSpan to override.

Serverless / short-lived environments (Vercel, AWS Lambda, Cloudflare Workers, edge): pass exportMode: "immediate" so spans are not held in a batch, and await langfuseSpanProcessor.forceFlush() before the function instance is frozen or terminated (e.g. inside Vercel's after() or the platform's waitUntil()). Spans still buffered when the process exits are lost.

Packages

Package	Description	Environments
@langfuse/tracing	OpenTelemetry-based tracing instrumentation	Node.js 20+
@langfuse/otel	`LangfuseSpanProcessor` to export OpenTelemetry spans to Langfuse	Node.js 20+
@langfuse/client	Prompt management, datasets, experiments, scores, full REST API	Universal JS
@langfuse/openai	`observeOpenAI` wrapper for tracing the OpenAI SDK	Universal JS
@langfuse/langchain	`CallbackHandler` for LangChain / LangGraph tracing	Universal JS
@langfuse/vercel-ai-sdk	Telemetry integration for Vercel AI SDK v7	Universal JS
@langfuse/browser	Browser score ingestion with public-key auth	Browser
@langfuse/core	Shared core: generated API client, logger, utilities	Universal JS