Streamdown includes built-in caret (cursor) indicators that display at the end of streaming content. Carets provide a visual cue to users that content is actively being generated, similar to a blinking cursor in a text editor.

The caret prop adds a visual indicator at the end of your streaming markdown content. This feature enhances the user experience by making it clear when content is actively being generated versus when generation is complete.

Key features:

• Two built-in styles - Choose between block (▋) and circle (●) carets
• Automatic positioning - Carets automatically appear at the end of the last rendered element
• Streaming-aware - Only displays when isAnimating={true} and mode="streaming" (default)
• CSS-based - Uses CSS custom properties and pseudo-elements for efficient rendering

To enable carets, pass the caret prop with either "block" or "circle":

import { Streamdown } from 'streamdown';

function StreamingChat() {
  const [isStreaming, setIsStreaming] = useState(true);
  const [content, setContent] = useState('');

  return (
    <Streamdown
      caret="block"
      isAnimating={isStreaming}
    >
      {content}
    </Streamdown>
  );
}

Streamdown provides two built-in caret styles:

Block Caret

The block caret displays a vertical bar (▋) similar to a terminal cursor:

<Streamdown caret="block" isAnimating={true}>
  Streaming content...
</Streamdown>

Circle Caret

The circle caret displays a filled circle (●) for a subtler indicator:

<Streamdown caret="circle" isAnimating={true}>
  Streaming content...
</Streamdown>

The caret visibility is controlled by two conditions:

1. caret prop is set - You must specify either "block" or "circle"
2. isAnimating={true} - The caret only appears during active streaming

When streaming stops (when isAnimating becomes false), the caret automatically disappears, leaving only the completed content.

Streamdown doesn't know about roles or message ordering, so you should conditionally show carets for specific messages, such as only displaying them for the last message in a chat and only displaying them from assistant messages:

{messages.map((message, index) => (
  <Streamdown
    key={message.id}
    caret={
      message.role === 'assistant' &&
      index === messages.length - 1
        ? 'block'
        : undefined
    }
    isAnimating={isStreaming}
  >
    {message.content}
  </Streamdown>
))}

Carets are implemented using CSS custom properties and pseudo-elements:

• The caret value is passed as a CSS custom property (--streamdown-caret)
• A ::after pseudo-element is added to the last child element
• The pseudo-element displays the caret character inline
• When isAnimating becomes false or caret is undefined, the styles are removed

This approach ensures efficient rendering without additional DOM elements.