Langfuse

Langfuse is an open-source LLM observability platform providing tracing, prompt management, evaluations, datasets, and analytics. It is framework-agnostic and can be fully self-hosted for free (nearly all features are MIT-licensed) or used as a managed cloud service. It was acquired by ClickHouse in January 2026.

Langfuse is an open-source engineering platform for observing, debugging, and improving LLM applications. It captures detailed traces of LLM calls, chains, and agent steps, so teams can see exactly what happened in a request, including inputs, outputs, latency, token usage, and cost. On top of tracing it provides prompt management with versioning, evaluations (including LLM-as-judge and human annotation), datasets, a playground, and analytics dashboards. A key part of Langfuse's appeal is that it is framework-agnostic and unusually generous with open source. In mid-2025 the company moved effectively all product features to the MIT license, leaving only thin enterprise compliance features (such as SCIM, audit logs, and fine-grained RBAC) as commercial. This makes self-hosting the full product genuinely viable, with no seat caps, retention limits, or usage caps, which distinguishes it from many observability tools whose open-source editions are heavily gated. Langfuse offers a managed cloud with a free tier and paid Core and Pro plans, plus self-hosting for free and an enterprise self-host license. It was acquired by ClickHouse in January 2026, a natural fit given Langfuse already used ClickHouse for its trace storage. It competes with LangSmith and other LLM observability tools, differentiating on open-source depth and self-hosting freedom.