Arize Phoenix

Phoenix is an open-source observability tool from Arize for LLM and agent applications. It records traces of every model call, retrieval step and tool use, then lets you inspect them in a local or hosted UI. Built-in evaluators score outputs for things like relevance and hallucination.

It runs in a notebook or a container with no account needed, which makes it quick to adopt during development. It follows OpenTelemetry conventions, so it fits with existing monitoring.

Teams often start with Phoenix while prototyping and move to Arize's paid platform when they need production-scale monitoring.