Langfuse
Observability & evalsAn open-source platform for tracing, evaluating, and monitoring LLM and agent applications.
Langfuse gives an AI system the observability that ordinary software takes for granted: every call, prompt, tool use, and agent step is traced, with cost and latency attached.
On top of tracing it adds evaluation and prompt management, and it is open-source and self-hostable — so the record of what your AI did can stay inside your perimeter.
Where it's ideally used
A strong default whenever an AI system reaches production and you need to see what it actually did, call by call.
Where it doesn't fit
More than a one-off script or a quick prototype needs — instrument once the system is real.