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Two ways to drive AgentX from Claude Code: the AgentX plugin (instrument → evaluate → fix as slash commands, plus /auto-improve for applying confirmed production failures), and the improve-prompt skill (the Prompt Management loop with Claude’s own reasoning standing in for the server-side judge call).

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The AgentX plugin

One plugin, one loop: get an agent’s real runs into AgentX, score them, then turn what they measure into a code fix. Install it from the plugin marketplace:
The seam between the commands is the point: an evaluation result carrying a traceId is judged against the agent’s real execution path, where one without it is judged on answer text alone. All three commands talk to a local self-host engine (normally http://localhost:4700) - see Installation to get one running.

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The improve-prompt skill

Prompt Management’s Suggest improvement needs a provider key (OPENAI_API_KEY/ANTHROPIC_API_KEY/GEMINI_API_KEY) set on the engine, since it makes a real judge call server-side. If you don’t have one configured - or you’re already working in Claude Code anyway - there’s a second way in, the same idea as Langfuse’s Claude-skill prompt-improvement workflow: Claude’s own reasoning stands in for the judge call, so no engine-side LLM key is needed at all.

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Setup

Copy the skill from AgentX-trace-eval/skills/improve-prompt into .claude/skills/improve-prompt/ in whatever project you run Claude Code from (your own agent’s repo works fine - the skill only talks to your self-host engine over HTTP). Then, with your engine running:

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What it does

Claude reads the prompt’s real worst-rated eval results straight from your engine (GET /api/v1/evaluate/prompts/:id/examples - the same evidence Suggest improvement uses, just without a judge call in front of it), drafts a full rewrite and explains what changed and why, and shows you both versions side by side. It never publishes on its own - only once you say something like “publish it” does it call the same POST /api/v1/evaluate/prompts/:id/versions the dashboard button uses. It finds your engine automatically: the API key comes straight from ~/.agentx/config.json (written the first time you start the engine), and the base URL defaults to AGENTX_API_BASE_URL - the same variable the SDK itself reads - falling back to http://localhost:4700/api/v1.