LangFuse LangChain

LangFuse LangChain is a callback integration that passes every request, tool invocation, and LLM token from a LangChain pipeline to LangFuse, an open-source observability and analytics platform for generative AI. You install langfuse and register a LangFuseCallbackHandler(api_key, project_id) inside your chain or agent. The handler automatically logs request inputs, model outputs, latencies, costs, and user feedback, then visualizes traces in the LangFuse web UI with flame-graph timelines and heat-map token usage. Built-in dashboards track success rates, hallucination flags, and RAG document overlaps, while A/B experiments compare request versions or model replacements. Alerts are triggered when latency spikes or cost thresholds are exceeded, sending notifications to Slack or PagerDuty. By combining LangChain’s deep telemetry with LangFuse’s analytics, teams transform opaque LLM workflows into measurable, debuggable, and optimizable services, reducing iteration cycles from days to minutes.