> ## Documentation Index
> Fetch the complete documentation index at: https://fastmcp-ts.docs.prefect.io/llms.txt
> Use this file to discover all available pages before exploring further.

# RouteMapFn

```ts theme={null}
type RouteMapFn = (route, mcpType) => MCPType | null | undefined;
```

Defined in: [server/openapi/types.ts:103](https://github.com/PrefectHQ/fastmcp-ts/blob/main/src/server/openapi/types.ts#L103)

Advanced route-type hook, run after the route maps on every non-excluded
route. Return a new MCPType to override, or null/undefined to keep the
mapped type. Exceptions are swallowed with a warning.

## Parameters

### route

[`HTTPRoute`](/api/server/interfaces/HTTPRoute)

### mcpType

[`MCPType`](/api/server/type-aliases/MCPType)

## Returns

[`MCPType`](/api/server/type-aliases/MCPType) | `null` | `undefined`