Phoenix

Arize Phoenix is an open source observability and evaluation tool for AI agents and LLM applications. It lets engineers trace what an application did, evaluate the quality of its outputs, run experiments and compare results, and debug failures. It can run locally with a single command or be self hosted inside a team's own environment, and the vendor also points to a hosted Phoenix Cloud option. Phoenix is the open source side of Arize, which also sells Arize AX, a managed AI engineering platform. Phoenix is built on OpenTelemetry instrumentation, and the site offers an install path that uses a coding agent to add tracing to an existing project. The vendor's documentation covers the setup guide and the evaluation features. It is aimed at developers and AI engineering teams who need visibility into agent behavior and a repeatable way to test changes before and after release. Pricing applies to the managed Arize AX product rather than to the self hosted software. AX Free costs nothing and includes 25,000 trace spans and 1 GB of ingestion per month, with 15 days of retention and unlimited users and evals. AX Pro costs $50 per month and raises that to 50,000 spans, 10 GB of ingestion and 30 days of retention. AX Enterprise is custom priced and can be deployed as software as a service or self hosted, and startup pricing is also offered.