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

# XLSX & Custom Data Formats

## Custom File Loaders

HelloCSV supports integrating data formats different from standard CSV / TSV uploads by allowing developers to create a `CustomFileLoader`

```tsx theme={null}
interface CustomFileLoader {
  mimeType: string;
  label: string;
  convert: (
    loadEvent: ProgressEvent<FileReader>,
    file: File
  ) =>
    | {
        fileName: string;
        csvData: string;
      }
    | Promise<{
        fileName: string;
        csvData: string;
      }>;
}
```

A `CustomFileLoader` is responsible for parsing a file, of a target `mimeType`, and returning a `csvData` string, which then gets passed
to the rest of the pipeline.

The `convert` function supports returning a promise for parsing files server-side if needed.

### Usage

See [customFileLoader](https://hellocsv.mintlify.app/v0.4.3/api-reference/importer-props#customfileloaders) prop.