Observability for VoltAgent with Langfuse

Create a VoltAgent project

If you don’t have a VoltAgent project yet, you can create one using the VoltAgent CLI:

npm create voltagent-app@latest

Move into the project directory:

cd my-voltagent-app

You can get the full VoltAgent installation instructions here

Set up Langfuse project

Create a project in Langfuse and get your API keys from the project settings page.

Add environment variables

Create or update your .env.development file with the following variables:

# Your LLM API key
OPENAI_API_KEY=your-api-key
 
# Langfuse credentials
LANGFUSE_SECRET_KEY=sk-lf-...
LANGFUSE_PUBLIC_KEY=pk-lf-...
LANGFUSE_BASE_URL=https://cloud.langfuse.com # Optional. Defaults to https://cloud.langfuse.com

Install the @voltagent/langfuse-exporter package

Add the @voltagent/langfuse-exporter package to your project:

npm install @voltagent/langfuse-exporter

Configure Langfuse Exporter

Modify your main application file (e.g., index.ts where VoltAgent is initialized) to import LangfuseExporter and configure it within the VoltAgent options:

import { VoltAgent, Agent } from "@voltagent/core";
import { VercelAIProvider } from "@voltagent/vercel-ai";
import { openai } from "@ai-sdk/openai";
 
import { LangfuseExporter } from "@voltagent/langfuse-exporter";
 
const langfuseExporter = new LangfuseExporter({
  publicKey: process.env.LANGFUSE_PUBLIC_KEY,
  secretKey: process.env.LANGFUSE_SECRET_KEY,
  baseUrl: process.env.LANGFUSE_BASE_URL,
});
 
const agent = new Agent({
  name: "my-voltagent-app",
  description: "A helpful assistant that answers questions without using tools",
  llm: new VercelAIProvider(),
  model: openai("gpt-4o-mini"),
});
 
new VoltAgent({
  agents: {
    agent,
  },
  telemetryExporter: langfuseExporter,
});

Run your VoltAgent application

Start the VoltAgent development server or run your application as usual:

npm run dev

When you run the dev command, tsx will compile and run your code. You should see the VoltAgent server startup message in your terminal:

══════════════════════════════════════════════════
  VOLTAGENT SERVER STARTED SUCCESSFULLY
══════════════════════════════════════════════════
  ✓ HTTP Server: http://localhost:3141
 
  Developer Console:    https://console.voltagent.dev
══════════════════════════════════════════════════
[VoltAgent] All packages are up to date

Your agent is now running! To interact with it:

1. Open the Console: Click the https://console.voltagent.dev link in your terminal output (or copy-paste it into your browser).
2. Find Your Agent: On the VoltAgent Console page, you should see your agent listed (e.g., “my-agent”).
3. Open Agent Details: Click on your agent’s name.
4. Start Chatting: On the agent detail page, click the chat icon in the bottom right corner to open the chat window.
5. Send a Message: Type a message like “Hello” and press Enter.

View traces in Langfuse

Head over to your Langfuse dashboard and you’ll see the traces from your agent interactions. You can analyze the prompts, completions, and other details of your AI interactions.

Here’s an example of a trace: