# X_EVAL_TOOL_UNDOUBLED

## Means

an agent eval called a tool with no double

## Typical cause

an agent eval's model called a tool the defineEval declares no double for, and an eval never runs a real tool

## Fix

`add the tool to tools: on the defineEval, e.g. tools: { lookupOrder: (input) => ({ status: 'shipped' }) }`

[MCP and AI](/error-codes#mcp-and-ai)