# Debug Mode
> Debug mode for development and troubleshooting Svelte Virtual List
**Source:** [https://virtuallist.svelte.page/docs/debug](https://virtuallist.svelte.page/docs/debug)
---
Debug mode provides detailed information about the virtual list's internal state, useful for development and troubleshooting.
## Enabling Debug Mode
### Via Props
```svelte
{#snippet renderItem(item)}
{item.text}
{/snippet}
```
### Via Environment Variable
```bash
PUBLIC_SVELTE_VIRTUAL_LIST_DEBUG=true
```
## Debug Information
When enabled, the component provides:
| Property | Description |
|----------|-------------|
| `startIndex` | First rendered item index |
| `endIndex` | Last rendered item index |
| `totalItems` | Total items in the list |
| `visibleItemsCount` | Number of items currently visible |
| `processedItems` | Items with measured heights |
| `averageItemHeight` | Calculated average height |
| `atTop` | Whether scrolled to top |
| `atBottom` | Whether scrolled to bottom |
| `totalHeight` | Total calculated content height |
## Custom Debug Handler
Capture debug info programmatically:
```svelte
{#snippet renderItem(item)}
{item.text}
{/snippet}
```
## Visual Overlay
When `debug={true}`, a visual overlay displays real-time stats in the corner of the viewport.