Langfuse

Export server traces through Langfuse instrumentation

Langfuse registers an OpenTelemetry trace exporter for the app’s Node.js runtime.

Installation

Add the plugin

bunx chat-js@alpha add langfuse

The CLI installs the instrumentation source and generates its registration. This plugin adds no database tables or client UI.

Configure credentials

Set your Langfuse project keys in the app environment:

LANGFUSE_PUBLIC_KEY=your_public_key
LANGFUSE_SECRET_KEY=your_secret_key

Restart the app after configuring credentials. The plugin registers the exporter when instrumentation starts in the Node.js runtime and uses the application prefix as the service name. It skips registration in the Playwright test environment.

Options

Environment variable	Required	Purpose
`LANGFUSE_PUBLIC_KEY`	Yes	Project public key
`LANGFUSE_SECRET_KEY`	Yes	Project secret key
`LANGFUSE_BASE_URL`	No	Override the exporter’s service URL
`LANGFUSE_DEBUG`	No	Set to `true` to enable exporter debugging

Customization

Edit chatjs/plugins/langfuse/instrumentation.ts to change exporter registration and credentials.ts to change environment handling. The server factory declares the instrumentation contribution. See the Plugin API.