# X_MCP_CATALOG_UNRESOLVED

## Means

a per-caller MCP catalog could not be resolved

## Typical cause

defineAppMcp({ catalog }) threw, or answered something other than { tools: runtimeTool()[] } this server can serve

## Fix

`defineAppMcp({ catalog: (caller) => ({ tools: [runtimeTool({ name, description, inputSchema, permission, run })] }) })` — fix what the cause names in the catalog function: its throw, an entry not built by `runtimeTool()`, or a scope the boot `scopes:` map does not declare

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