langfuse-local-dev-loop

name	langfuse-local-dev-loop
description	Set up Langfuse local development workflow with hot reload and debugging. Use when developing LLM applications locally, debugging traces, or setting up a fast iteration loop with Langfuse. Trigger with phrases like "langfuse local dev", "langfuse development", "debug langfuse traces", "langfuse hot reload", "langfuse dev workflow".
allowed-tools	Read, Write, Edit, Bash(npm:*), Bash(docker:*), Bash(pnpm:*)
version	1.12.0
license	MIT
author	Jeremy Longshore <[e-mail]>
tags	["saas","langfuse","llm","debugging","workflow"]
compatibility	Designed for Claude Code

Langfuse Local Dev Loop

Overview

Fast local development workflow with Langfuse tracing, immediate trace visibility, debug logging, and optional self-hosted local instance via Docker.

Prerequisites

• Completed langfuse-install-auth setup
• Node.js 18+ with tsx for hot reload (npm install -D tsx)
• Docker (optional, for self-hosted local instance)

Instructions

Step 1: Development Environment File

# .env.local (git-ignored)
LANGFUSE_PUBLIC_KEY=pk-lf-dev-...
LANGFUSE_SECRET_KEY=sk-lf-dev-...
LANGFUSE_BASE_URL=https://cloud.langfuse.com

# Dev-specific settings
NODE_ENV=development
OPENAI_API_KEY=sk-...

Step 2: Dev-Optimized Langfuse Setup (v4+)

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

const isDev = process.env.NODE_ENV !== "production";

// Configure span processor with dev-friendly settings
const processor = new LangfuseSpanProcessor({
  // In dev: flush immediately for instant visibility
  ...(isDev && { exportIntervalMillis: 1000, maxExportBatchSize: 1 }),
});

const sdk = new NodeSDK({ spanProcessors: [processor] });
sdk.start();

  langfuse =  ();


  () {
   (isDev) {
     host = process.. || ;
    .();
  }
}


process.(,  () => {
   sdk.();
  process.();
});