Arize Phoenix

Arize Phoenix is the open-source observability and evaluation tool from Arize AI. For a technical founder building an AI product, it gives you a free way to inspect traces, debug LLM behavior, run evaluations, and understand why an application produced a bad answer.

The fit is especially good when you are not ready to pay for a full observability platform but you already feel the pain of invisible agent behavior. Phoenix lets you start locally or self-host, then move toward Arize’s managed platform when production volume, retention, monitors, or team workflows become the bottleneck.

Set expectations correctly: Phoenix is not a point-and-click agent for a business operator. It is infrastructure for builders. If you are wiring agents into your own app, it is a low-cost way to get serious about traces and evals before the first real incident teaches you why they matter.