langfuse-install-auth

Install and configure Langfuse SDK authentication for LLM observability. Use when setting up a new Langfuse integration, configuring API keys, or initializing Langfuse tracing in your project. Trigger with phrases like "install langfuse", "setup langfuse", "langfuse auth", "configure langfuse API key", "langfuse tracing setup".

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name	langfuse-install-auth
description	Install and configure Langfuse SDK authentication for LLM observability. Use when setting up a new Langfuse integration, configuring API keys, or initializing Langfuse tracing in your project. Trigger with phrases like "install langfuse", "setup langfuse", "langfuse auth", "configure langfuse API key", "langfuse tracing setup".
allowed-tools	Read, Write, Edit, Bash(npm:), Bash(pip:), Bash(pnpm:*), Grep
version	1.12.0
license	MIT
author	Jeremy Longshore <jeremy@intentsolutions.io>
tags	["saas","langfuse","api","observability","llm"]
compatibility	Designed for Claude Code

Langfuse Install & Auth

Overview

Install the Langfuse SDK and configure authentication for LLM observability. Covers both the legacy langfuse package (v3) and the modern modular SDK (v4+/v5) built on OpenTelemetry.

Prerequisites

Node.js 18+ or Python 3.9+
Package manager (npm, pnpm, or pip)
Langfuse account (cloud at https://cloud.langfuse.com or self-hosted)
Public Key (pk-lf-...) and Secret Key (sk-lf-...) from project settings

Instructions

Step 1: Install SDK

TypeScript/JavaScript (v4+ modular SDK -- recommended):

set -euo pipefail
# Core client for prompt management, datasets, scores
npm install @langfuse/client

# Tracing (observe, startActiveObservation)
npm install @langfuse/tracing @langfuse/otel @opentelemetry/sdk-node

# OpenAI integration (drop-in wrapper)
npm install @langfuse/openai

# LangChain integration
npm install @langfuse/langchain

TypeScript/JavaScript (v3 legacy -- single package):

npm install langfuse

Python:

pip install langfuse

Step 2: Get API Keys

Open Langfuse dashboard (https://cloud.langfuse.com or your self-hosted URL)
Go to Settings > API Keys
Click Create new API key pair
Copy both keys:
- Public Key: pk-lf-... (identifies your project)
- Secret Key: sk-lf-... (grants write access -- keep secret)
Note the host URL (cloud default: https://cloud.langfuse.com)

Step 3: Configure Environment Variables

# Set environment variables
export LANGFUSE_PUBLIC_KEY="pk-lf-..."
export LANGFUSE_SECRET_KEY="sk-lf-..."
 LANGFUSE_BASE_URL=


 >> . << 
LANGFUSE_PUBLIC_KEY=pk-lf-your-public-key
LANGFUSE_SECRET_KEY=sk-lf-your-secret-key
LANGFUSE_BASE_URL=https://cloud.langfuse.com
EOF

// src/lib/langfuse.ts
import { LangfuseClient } from "@langfuse/client";
import { startActiveObservation } from "@langfuse/tracing";
import { LangfuseSpanProcessor } from "@langfuse/otel";
import { NodeSDK } from "@opentelemetry/sdk-node";

// 1. Register the OpenTelemetry span processor (once at app startup)
const sdk = new NodeSDK({
  spanProcessors: [new LangfuseSpanProcessor()],
});
sdk.start();

// 2. Create the Langfuse client for prompt/dataset/score operations
export const langfuse = new LangfuseClient({
  publicKey: process.env.LANGFUSE_PUBLIC_KEY,
  secretKey: process.env.LANGFUSE_SECRET_KEY,
  baseUrl: process.env.LANGFUSE_BASE_URL,
});

// 3. Verify connection
async function verify() {
  await startActiveObservation("connection-test", async (span) => {
    span.update({ input: { test: true } });
    span.update({ output: { status: "connected" } });
  });
  console.log("Langfuse connection verified. Check dashboard for trace.");
}

verify();

import { Langfuse } from "langfuse";

const langfuse = new Langfuse({
  publicKey: process.env.LANGFUSE_PUBLIC_KEY,
  secretKey: process.env.LANGFUSE_SECRET_KEY,
  baseUrl: process.env.LANGFUSE_HOST,
});

// Verify with a test trace
const trace = langfuse.trace({
  name: "connection-test",
  metadata: { test: true },
});

await langfuse.flushAsync();
console.log("Connected. Trace URL:", trace.getTraceUrl());

// Clean shutdown
process.on("beforeExit", async () => {
  await langfuse.shutdownAsync();
});

from langfuse import Langfuse
import os

langfuse = Langfuse(
    public_key=os.environ["LANGFUSE_PUBLIC_KEY"],
    secret_key=os.environ["LANGFUSE_SECRET_KEY"],
    host=os.environ.get("LANGFUSE_HOST", "https://cloud.langfuse.com"),
)

# Test trace
trace = langfuse.trace(name="connection-test", metadata={"test": True})
langfuse.flush()
print(f"Connected. Trace: {trace.get_trace_url()}")

Feature	v3 (`langfuse`)	v4+ (`@langfuse/*`)
Package	Single `langfuse`	Modular: `@langfuse/client`, `@langfuse/tracing`, `@langfuse/otel`
Base URL env var	`LANGFUSE_HOST`	`LANGFUSE_BASE_URL`
Tracing	`langfuse.trace()`	`startActiveObservation()` / `observe()`
Client class	`Langfuse`	`LangfuseClient`
OpenAI wrapper	`observeOpenAI()` from `langfuse`	`observeOpenAI()` from `@langfuse/openai`
Foundation	Custom	OpenTelemetry

Error	Cause	Solution
`401 Unauthorized`	Invalid or expired API key	Re-check keys in Langfuse dashboard Settings > API Keys
`ECONNREFUSED`	Wrong host URL or server down	Verify `LANGFUSE_BASE_URL` / `LANGFUSE_HOST`
`Missing required configuration`	Env vars not loaded	Ensure `dotenv/config` imported at entry point
`Module not found`	Package not installed	Run `npm install` or `pip install` again
Using pk- key as secret	Keys swapped	Public key starts `pk-lf-`, secret starts `sk-lf-`