Langfuse

Langfuse is an open-source LLM observability and evaluation platform that gives you visibility into what your AI application is actually doing. As soon as you build on large language models, things become opaque — prompts misbehave, costs spike, latency creeps up — and Langfuse solves that with rich, detailed tracing of every request, including complex multi-step chains and agents, so you can see exactly how a request flowed through your prompts, tools and model calls.

Beyond tracing, Langfuse is built for serious LLM engineering. It offers a strong feature set for evaluation and experimentation: testing prompt versions, scoring outputs, running evals and systematically improving your AI's quality over the full lifecycle, not just watching requests go by. You can monitor cost and latency, debug failures, and measure whether changes actually make your app better. Because it is open source with a self-hosting option, you can keep sensitive prompt and response data entirely under your own control — a key advantage for privacy-conscious teams.

Langfuse is ideal for developers and teams doing real LLM engineering — building complex chains or agents and wanting both deep tracing and rigorous, structured evaluation. It is a leading option alongside tools like Helicone, with its depth of tracing and evals as its distinguishing strength. If you are running AI features in production and want to understand, debug and continuously improve them rather than flying blind, Langfuse provides the observability and quality tooling that modern AI applications increasingly require, all on an open foundation you can trust and own.