> ## Documentation Index
> Fetch the complete documentation index at: https://colin-feat-client-cache-mode.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# OnTokenCallback

```ts theme={null}
type OnTokenCallback = (token) => void;
```

Defined in: [client/sampling/types.ts:13](https://github.com/PrefectHQ/fastmcp-ts/blob/8976c37f79efa6b87809b884f29a1f235a8c4ad1/src/client/sampling/types.ts#L13)

Called with each text token as it is streamed from the provider.

## Parameters

### token

`string`

## Returns

`void`