Langfuse

Langfuse is an open-source platform that helps teams understand what their language model apps are doing. It records traces of each request, including the steps in an agent run, and shows cost, latency and quality over time. It also includes prompt management with versioning, plus tools to score outputs by hand, with another model or with user feedback. Datasets and experiments let you compare changes before they reach users. You can self-host it for free or use the cloud version, which has a free tier and paid plans. Many teams pick it because it is open and not tied to a single framework.