Langfuse

Langfuse is an open-source LLM engineering platform for collaborative development, monitoring, evaluation, and debugging of AI applications. Built on OpenTelemetry for vendor-neutral tracing, it provides structured logs with multi-turn conversation support, prompt versioning with playground, and flexible evaluation through LLM-as-judge or custom metrics. Native SDKs for Python and JavaScript with 50+ framework integrations including LangChain, LlamaIndex, and OpenAI. Self-host with Docker in 5 minutes or use generous free cloud tier. Over 19,000 GitHub stars with MIT license.