# ListOptionsHtmlFormat
**Kind:** Interface
**Source:** [`packages/platform-fastify/interfaces/external/fastify-static-options.interface.ts`](https://github.com/nestjs/nest/blob/master/packages/platform-fastify/interfaces/external/fastify-static-options.interface.ts#L54)
**Part of:** [Platform Fastify](subsystem-packages-platform-fastify)
`ListOptionsHtmlFormat` configures directory listing output in HTML format for Fastify static file serving. It requires `format` to be the literal value `'html'` and provides a `render` function responsible for generating the HTML response content.
## Properties
| Property | Type |
|---|---|
| `format` | `'html'` |
| `render` | `ListRender` |
## Diagram
```mermaid
graph LR
A[Fastify Static Directory Listing] --> B[ListOptionsHtmlFormat]
B --> C[format: 'html']
B --> D[render: ListRender]
D --> E[Generated HTML Response]
```
## Usage
```ts
import type { ListOptionsHtmlFormat } from './interfaces/external/fastify-static-options.interface';
const directoryListingOptions: ListOptionsHtmlFormat = {
format: 'html',
render: (directories, files) => {
const directoryItems = directories
.map((directory) => `${directory.name}/`)
.join('');
const fileItems = files
.map((file) => `${file.name}`)
.join('');
return `
Directory listing
Files
${directoryItems}${fileItems}
`;
},
};
```
## AI Coding Instructions
- Set `format` exactly to `'html'`; other values do not satisfy `ListOptionsHtmlFormat`.
- Implement `render` using the `ListRender` signature expected by the Fastify static integration.
- Escape file names, paths, and other dynamic values before inserting them into generated HTML.
- Return complete, valid HTML when using this format so browsers can render the directory listing correctly.
- Use this interface when configuring HTML directory listings rather than JSON or plain-text listing formats.