Phoenix
Observability & evalsArize's open-source tool for tracing, evaluating, and debugging LLM and agent apps.
Phoenix, from Arize, is an observability and evaluation tool built on OpenTelemetry. It traces LLM and agent applications, runs evaluations, and is strong at the debugging end — inspecting and comparing runs to find where quality broke.
It self-hosts and runs locally, and pairs with Arize's larger production-monitoring platform.
Where it's ideally used
A fit when you want open, OpenTelemetry-based tracing and evaluation with a focus on debugging agent behaviour.
Where it doesn't fit
For long-term production monitoring at scale, the hosted Arize platform is the heavier sibling to grow into.