langfuse-hello-world

# Langfuse Hello World ## Overview Create your first Langfuse trace with real SDK calls. Demonstrates the trace/span/generation hierarchy, the `observe` wrapper, and the OpenAI drop-in integration. ## Prerequisites - Completed `langfuse-install-auth` setup - Valid API credentials in environment variables - OpenAI API key (for the OpenAI integration example) ## Instructions ### Step 1: Hello World with v4+ Modular SDK ```typescript // hello-langfuse.ts import { startActiveObservation, observe, updateActiveObservation } from "@langfuse/tracing"; import { LangfuseSpanProcessor } from "@langfuse/otel"; import { NodeSDK } from "@opentelemetry/sdk-node"; // Register OpenTelemetry processor (once at startup) const sdk = new NodeSDK({ spanProcessors: [new LangfuseSpanProcessor()], }); sdk.start(); async function main() { // Create a top-level trace with startActiveObservation await startActiveObservation("hello-world", async (span) => { span.update({ input: { message: "Hello, Langfuse!" }, metadata: { source: "hello-world-example" }, }); // Nested span -- automatically linked to parent await startActiveObservation("process-input", async (child) => { child.update({ input: { text: "processing..." } }); await new Promise((r) => setTimeout(r, 100)); child.update({ output: { result: "done" } }); }); // Nested generation (LLM call tracking) await startActiveObservation( { name: "llm-response", asType: "generatio...