Use the `maxlength` attribute to set a maximum length for the textarea to be valid.

```html
<div class="max-w-[500px]">
  <sd-textarea
    value=""
    size="lg"
    label="Label"
    help-text="You are limited to a maximum of 5 characters"
    rows="4"
    spellcheck=""
    maxlength="5"
  ></sd-textarea>
</div>
```