Langfuse is an open-source LLM observability and evaluation platform that helps AI engineering teams trace, monitor, evaluate, and debug their language model applications in production. It captures detailed traces of every LLM call, prompt version, and user interaction — providing the visibility needed to understand latency, cost, quality regressions, and user satisfaction across complex AI pipelines. AI product teams at startups and enterprises use Langfuse to systematically improve their LLM applications post-deployment, catching quality issues before they impact users and informing data-driven improvements to prompts and models.