Arize Phoenix MCP Server

Arize Phoenix is the open-source LLM observability and evaluation platform, and @arizeai/phoenix-mcp is its official Model Context Protocol server. It gives an assistant a single interface to the three things Phoenix stores: the traces your application emitted, the prompts you version, and the datasets and experiments you evaluate against.

The tool surface is unusually broad for an observability server — more than 30 tools across seven areas. Prompts get nine of them, including creating and updating versions, so an agent can iterate on a prompt and commit the result to Phoenix rather than leaving it in a scratch file. Traces and spans can be listed and read, span annotations retrieved, and sessions walked. Datasets support listing, reading, adding examples and enumerating the experiments run against them, and experiments can be listed and fetched by ID.

In practice that makes it a way to close the evaluate-and-improve loop from inside a coding agent: pull the failing spans, look at the prompt version that produced them, add the failures to a dataset as examples, and re-run the experiment — all without leaving the editor.

It runs over npx against either Phoenix Cloud or a self-hosted instance; point --baseUrl at your deployment and supply an API key. Apache 2.0 licensed, developed in the Phoenix monorepo at Arize-ai/phoenix.