Connect Your Coding Agent

Connect your coding agent to Phoenix so it can instrument your app, read the traces that come back, and act on what it finds.

Works with Claude Code, Codex, Cursor, or any other coding agent. Once connected, you ask in plain language:

Show me the latest traces in my default project and summarize any errors

Connect your agent

Agent	Setup
Claude Code	Install the Claude Code plugin. That is the MCP server and the Phoenix skills in one step. Optional: install the CLI so the agent can also run px commands.
Codex	Install the Codex plugin for the MCP server, then npx -y @arizeai/phoenix-cli setup skills for the skills.
Cursor, VS Code, Gemini CLI, OpenCode	Install the CLI, then run px setup mcp --agent <agent> and px setup skills.
Any other agent	Install the CLI, add the MCP server from its per-client steps, and install skills with npx skills add.

Then ask your agent a question, such as List my Phoenix projects.

Example prompts

Instrument an app:

Use the Phoenix tracing skill to instrument this application. First inspect the codebase and identify the LLM providers, frameworks, package manager, and existing OpenTelemetry setup. Then propose the Phoenix instrumentation plan before changing code.

Run the Evaluate flow end to end:

Download https://storage.googleapis.com/arize-phoenix-assets/assets/images/arize-docs-images/evaluate/travel-support.csv and create a Phoenix dataset called "travel-support" from it, mapping the question column to input and expected_answer to output. Then write an LLM-as-a-judge evaluator that scores whether a reply answers the question and matches the expected answer. Run an experiment over the dataset with a travel support prompt, and tell me which examples scored lowest and why.

Every example scores 0 on that first run: the prompt knows nothing about this airline. Then reply Add the Basic fare policy to the prompt, rerun the experiment, and compare the scores.

Find your Phoenix endpoint

Every setup needs your Phoenix endpoint: the base URL you open Phoenix at, with no trailing slash or path.

Deployment	Endpoint	MCP server URL the tools derive from it
Local Phoenix (phoenix serve)	http://localhost:6006	http://localhost:6006/mcp
Deployed Phoenix	https://phoenix.example.com (your deployment’s hostname)	https://phoenix.example.com/mcp

The plugins and px append /mcp themselves; only hand-written MCP config takes the full /mcp URL.

px and the Codex plugin read it from your shell:

export PHOENIX_ENDPOINT=http://localhost:6006    # Your Phoenix endpoint
export PHOENIX_PROJECT=my-project                # Project name
export PHOENIX_API_KEY=your-api-key              # API key (if auth enabled)

Plugins

The plugins bundle the MCP server and skills into one install that stays up to date. They need Phoenix 19.0.0 or later.

Claude Code plugin

Steps 1, 2, and 4 are slash commands inside a Claude Code session. If /plugin is not recognized, update Claude Code.

1. Add the marketplace

   /plugin marketplace add Arize-ai/phoenix
   
2. Install the plugin

   /plugin install arize-phoenix@arize-phoenix
   

   Claude Code asks for a scope: user for all your projects, project to share it with collaborators through .claude/settings.json, or local for this repository only.

3. Set your Phoenix endpoint

   Claude Code prompts for one setting, Phoenix endpoint, as it enables the plugin. Enter your Phoenix endpoint, or keep the default http://localhost:6006. The plugin appends /mcp itself, so a trailing slash or a pasted /mcp produces a wrong URL (…//mcp or …/mcp/mcp). This setting is stored in your user settings and applies to every project.

4. Verify

   Run /mcp and select phoenix. If your Phoenix has auth enabled, a browser window opens to sign in with your Phoenix account; without auth, it connects straight away.

   claude plugin details arize-phoenix@arize-phoenix lists what it added.

From a shell: claude plugin marketplace add Arize-ai/phoenix then claude plugin install arize-phoenix@arize-phoenix (add --scope project or --scope local to narrow it).

What it registers

Component	What it is
phoenix MCP server	Streamable HTTP to <your-endpoint>/mcp, the Remote MCP Server.
phoenix-cli skill	Fetching traces, inspecting datasets and experiments, and querying GraphQL with the px CLI.
phoenix-evals skill	Building and running evaluators.
phoenix-tracing skill	Instrumenting apps with OpenInference.

It does not install the px CLI; add that separately if you want it.

Change the endpoint. claude plugin install arize-phoenix@arize-phoenix --config endpoint=https://phoenix.example.com at install time, /plugin configure afterward, or edit ~/.claude/settings.json:

{
  "pluginConfigs": {
    "arize-phoenix@arize-phoenix": {
      "options": { "endpoint": "https://phoenix.example.com" }
    }
  }
}

Authentication. With auth on, the first use opens a browser sign-in. For headless use, register the server by hand with an API key instead.

Update or remove

claude plugin update arize-phoenix@arize-phoenix     # pull the latest version
claude plugin disable arize-phoenix@arize-phoenix    # keep it installed, turn it off
claude plugin uninstall arize-phoenix@arize-phoenix  # remove the plugin

Pass the scope you installed at, such as --scope local, to disable and uninstall.

Codex plugin

Registers the MCP server. Skills are separate: npx -y @arizeai/phoenix-cli setup skills.

Prerequisites: Phoenix 19.0.0 or later, and Node.js. The plugin starts its MCP bridge with npx. The codex plugin commands below run in your shell.

1. Add the marketplace

   codex plugin marketplace add Arize-ai/phoenix
   

   Codex clones the repository and reads the catalog from .agents/plugins/marketplace.json. The source can be owner/repo shorthand, owner/repo@ref, an HTTPS or SSH Git URL, or a local path; pass --ref to pin a Git ref.

2. Install the plugin

   codex plugin add arize-phoenix@arize-phoenix
   

   Codex caches the plugin under ~/.codex/plugins/cache/arize-phoenix/arize-phoenix/<version> and enables it in ~/.codex/config.toml. You can also browse and install from the /plugins browser inside Codex.

3. Export your Phoenix endpoint

   The plugin reads PHOENIX_ENDPOINT from the shell you launch Codex from:

   export PHOENIX_ENDPOINT=https://phoenix.example.com   # base URL only; the plugin appends /mcp
   export PHOENIX_API_KEY=your-api-key                   # only if auth is enabled
   

   Unset, it defaults to http://localhost:6006.

4. Verify

   codex mcp list
   

   The phoenix server appears as enabled. Then launch codex and run /mcp to confirm it connects. If your Phoenix has auth enabled and PHOENIX_API_KEY is not set, a browser window opens on first use to sign in; with the key set, or with auth disabled, no login happens.

Variable	Effect
PHOENIX_ENDPOINT	Base URL; /mcp is appended for you.
PHOENIX_API_KEY	Optional. Sent as a bearer token, so no browser login.

Disable or remove. In ~/.codex/config.toml:

[plugins."arize-phoenix@arize-phoenix"]
enabled = true

codex plugin marketplace upgrade arize-phoenix   # refresh the catalog snapshot
codex plugin remove arize-phoenix@arize-phoenix  # uninstall and clear the cache
codex plugin marketplace remove arize-phoenix    # drop the marketplace

Learn more

• Tracing coding agents: have Phoenix record your coding agent’s own turns, tool calls, and token costs.