# X_MCP_CATALOG_TOOL_DUPLICATE

## Means

a per-caller MCP catalog names one tool twice

## Typical cause

defineAppMcp({ catalog }) resolved a tool whose name a static tool, a meta tool, list_tenants or another runtime tool already answers to

## Fix

`defineAppMcp({ catalog: (caller) => ({ tools: [runtimeTool({ name: '<unique-name>', … })] }) }) — rename the runtime tool; x mcp tools --json lists the static names`

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