Langfuse

Langfuse is an open-source observability platform (MIT license) for LLM applications enabling complete tracing of LLM calls, versioned prompt management, and automated evaluation. The platform records every LLM call, inputs/outputs, and dependencies to provide complete visibility into AI agent and chain behavior. It includes an evaluation system (LLM-as-judge, custom scoring scripts, human annotations), dataset management for continuously testing prompts and models, and custom dashboards to track quality and costs. Acquired by ClickHouse in January 2026, the platform now benefits from that database's infrastructure for massive-scale processing. The free Hobby tier (50k units/month, 30d retention) lets you start cost-free; the Core plan ($29/month, 100k units, 90d retention) targets small projects; Pro ($199/month, 3-year retention, SOC2/ISO27001 compliance) and Enterprise ($2,499/month, dedicated support, custom pricing).

Langfuse does not provide a French-language interface and remains developer-oriented. The complete REST API and Python/TypeScript SDKs enable seamless integration into existing LLM stacks (LangChain, OpenAI SDK, Anthropic SDK, etc.) without application code modifications. The 'units'-based pricing model (traces plus observations plus scores) with overage pricing ($8/100k, decreasing at high volume) offers transparency and predictability if your consumption is estimable. The platform can also be self-hosted free (MIT license) for teams wanting independence from cloud providers. The learning curve is low for developers familiar with the LLM ecosystem; the main limitation is the absence of no-code UI for business profiles.