Helicone
Open-source LLM observability platform. One-line integration to log every LLM request, track costs, and debug slow or failing calls.
Langfuse
Open-source platform for tracing, evaluations, and prompt management. Self-hostable alternative to LangSmith with broad framework support. Acquired by ClickHouse in January 2026; OSS core continues with deeper ClickHouse-backed analytics.