Langfuse is an open source LLM engineering platform that enables teams to develop, debug, and improve their AI applications in production. It rests on four complementary modules: observability (complete tracing of LLMs and agents via OpenTelemetry), prompt management (versioning, playground, experiments), evaluation (LLM-as-judge, human annotation, datasets, regression tests), and metrics (costs, latencies, user feedback). Compatible with Python, JavaScript, Java, and Go, Langfuse integrates natively with LangChain, LlamaIndex, LiteLLM, OpenAI, and dozens of other frameworks. Fully self-hostable on any infrastructure, certified SOC 2 Type II and ISO 27001, the platform is used by Khan Academy, Twilio, Merck, and thousands of teams worldwide.
What is Langfuse?
Langfuse is an open source LLM engineering platform that covers the entire lifecycle of an AI application in production. It is structured around four main modules: observability (complete tracing of LLM calls and agent workflows), prompt management (versioning, playground, experiments), evaluation (automated and human evaluations, datasets, regression tests), and metrics (costs, latencies, user feedback, usage). The platform is based on the OpenTelemetry standard and integrates natively with major LLM frameworks on the market.
Key Features
Langfuse groups four complementary modules. Observability captures complete traces of each LLM call and each agent workflow, with native support for Python, JavaScript, Java, and Go. It allows tracking conversation sessions, individual users, tokens, and costs per request. The prompt management module offers versioning, release management, composability (nested prompts), server and client-side caching, an interactive playground, and A/B experiments. The evaluation module provides configurable LLM-as-judge evaluators, human annotation with review queues, dataset management for regression tests, experiments via SDK and UI, and external evaluation pipelines. Finally, metrics provide dashboards on costs, latency, quality, and usage by feature, with integrations to PostHog and Mixpanel.
Use Cases
Langfuse adapts to many concrete use cases. For production debugging, teams quickly identify problematic traces by filtering on latency, cost, or quality score. For continuous prompt improvement, teams iterate on versions with A/B experiments anchored on historical test datasets. For chatbots and assistants, Langfuse traces complete sessions and enables analyzing problematic conversations. For complex agent workflows, it visualizes execution graphs with each tool call and decision traced. For regulated sectors like healthcare and finance, it provides necessary compliance with data stored in Europe or the United States.
Advantages
Langfuse provides several decisive advantages. The open source nature guarantees freedom from vendor lock-in and enables auditing the code in full transparency. Self-hosting offers complete data control, essential for organizations with strict sovereignty requirements. OpenTelemetry compliance facilitates integration into existing technical stacks and avoids costly migrations. The combination of observability + evaluations + prompt management in a single platform eliminates the need to manage multiple tools. The generous free plan allows startups and open source projects to start without budget constraints.
Pricing
Langfuse offers four pricing tiers. The Hobby plan is free with 50,000 units/month, 30-day retention, and 2 users, without a credit card. The Core plan at $29/month scales to 100,000 units/month, 90-day retention, and unlimited users. The Pro plan at $199/month offers 3 years retention, very high request rates, and SOC 2/HIPAA compliance. The Enterprise plan at $2,499/month targets large organizations with custom limits, dedicated SLA, and priority support. Self-hosting is available free for all plans with open source code.
Conclusion
Langfuse is today the most comprehensive and widely adopted open source LLM engineering platform. Its combination of observability, evaluations, and prompt management in a single self-hostable solution makes it the strategic choice for any team taking the quality of their production LLM applications seriously. The free plan lets you start immediately, and advanced compliance meets the needs of the most regulated sectors.