Langfuse is an open-source product analytics tool designed for LLM applications, aimed at addressing the unique challenges of tracking and analyzing quality, cost, and latency in these complex software environments. Developed by Max, Marc, and Clemens as part of the Winter 2023 YC batch, Langfuse helps companies monitor how LLM applications perform by offering insights into user behavior and application outputs, which can often be inaccurate or poorly formatted. It measures quality through user feedback and model-based scoring, while also providing detailed metrics on cost and latency, broken down by various parameters such as user and geography. Langfuse offers integrations through Python and Typescript SDKs for easy monitoring and a frontend SDK for capturing user feedback. Its debugging UI helps developers inspect app executions and troubleshoot quality issues, and the platform can be self-hosted or used via a managed cloud version with a free tier.