Langfuse is an open-source LLM engineering platform that helps teams develop, monitor, evaluate, and debug production LLM applications. It captures traces of model requests and responses, runs evaluations (evals), manages and versions prompts, and exposes metrics and dashboards to track model performance and behavior. Langfuse integrates with popular LLM stacks such as LangChain, OpenAI, LlamaIndex, and LiteLLM, enabling teams to add observability and evaluation into existing workflows. Its open-source design supports self-hosting and collaborative development for teams building production-grade LLM systems.