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

# useDownloadFile

> Download files through the host.

<Badge color="yellow">sunpeak API</Badge>

## Overview

Returns a function to download files through the host. Since MCP Apps run in sandboxed iframes where direct downloads are blocked, this provides a host-mediated mechanism for file exports.

Supports embedded text content, embedded binary (base64) content, and resource links that the host fetches on behalf of the app.

<Card horizontal title="Wraps downloadFile" icon="cube" href="/mcp-apps/app/requests/download-file">
  MCP Apps SDK reference
</Card>

## Import

```tsx theme={null}
import { useDownloadFile } from 'sunpeak';
```

## Signature

```tsx theme={null}
function useDownloadFile(): (params: DownloadFileParams) => Promise<DownloadFileResult | undefined>
```

### DownloadFileParams

<ResponseField name="contents" type="(EmbeddedResource | ResourceLink)[]" required>
  Resource contents to download — embedded (inline data) or linked (host fetches).
</ResponseField>

## Returns

<ResponseField name="downloadFile" type="(params: DownloadFileParams) => Promise<DownloadFileResult | undefined>">
  Function to request a file download through the host.
</ResponseField>

### DownloadFileResult

<ResponseField name="isError" type="boolean">
  Whether the download failed (e.g. user cancelled or host denied).
</ResponseField>

## Usage

### Embedded text content

```tsx theme={null}
import { useDownloadFile } from 'sunpeak';

function ExportButton({ data }: { data: unknown }) {
  const downloadFile = useDownloadFile();

  return (
    <button onClick={() => downloadFile({
      contents: [{
        type: 'resource',
        resource: {
          uri: 'file:///export.json',
          mimeType: 'application/json',
          text: JSON.stringify(data, null, 2),
        },
      }],
    })}>
      Export JSON
    </button>
  );
}
```

### Resource link (host fetches)

```tsx theme={null}
const downloadFile = useDownloadFile();

await downloadFile({
  contents: [{
    type: 'resource_link',
    uri: 'https://api.example.com/reports/q4.pdf',
    name: 'Q4 Report',
    mimeType: 'application/pdf',
  }],
});
```