Streamdown

A drop-in replacement for react-markdown, designed for AI-powered streaming.

Overview

Formatting Markdown is easy, but when you tokenize and stream it, new challenges arise. Streamdown is built specifically to handle the unique requirements of streaming Markdown content from AI models, providing seamless formatting even with incomplete or unterminated Markdown blocks.

Streamdown powers the AI Elements Response component but can be installed as a standalone package for your own streaming needs.

Features

• 🚀 Drop-in replacement for react-markdown
• 🔄 Streaming-optimized - Handles incomplete Markdown gracefully
• 🎨 Unterminated block parsing - Styles incomplete bold, italic, code, links, and headings
• 📊 GitHub Flavored Markdown - Tables, task lists, and strikethrough support
• 🔢 Math rendering - LaTeX equations via KaTeX
• 📈 Mermaid diagrams - Render Mermaid diagrams as code blocks with a button to render them
• 🎯 Code syntax highlighting - Beautiful code blocks with Shiki
• 🛡️ Security-first - Built with rehype-harden for safe rendering
• ⚡ Performance optimized - Memoized rendering for efficient updates

Installation

npm i streamdown

Then, update your Tailwind globals.css to include the following.

@source "../node_modules/streamdown/dist/index.js";

Make sure the path matches the location of the node_modules folder in your project. This will ensure that the Streamdown styles are applied to your project.

Usage

Basic Example

import { Streamdown } from 'streamdown';

export default function Page() {
  const markdown = "# Hello World\n\nThis is **streaming** markdown!";

  return <Streamdown>{markdown}</Streamdown>;
}

Mermaid Diagrams

Streamdown supports Mermaid diagrams using the mermaid language identifier:

import { Streamdown } from 'streamdown';
import type { MermaidConfig } from 'mermaid';

export default function Page() {
  const markdown = `
# Flowchart Example

\`\`\`mermaid
graph TD
    A[Start] --> B{Is it working?}
    B -->|Yes| C[Great!]
    B -->|No| D[Debug]
    D --> B
\`\`\`

# Sequence Diagram

\`\`\`mermaid
sequenceDiagram
    participant User
    participant API
    participant Database

    User->>API: Request data
    API->>Database: Query
    Database-->>API: Results
    API-->>User: Response
\`\`\`
  `;

  // Optional: Customize Mermaid theme and colors
  const mermaidConfig: MermaidConfig = {
    theme: 'dark',
    themeVariables: {
      primaryColor: '#ff0000',
      primaryTextColor: '#fff'
    }
  };

  return (
    <Streamdown mermaidConfig={mermaidConfig}>
      {markdown}
    </Streamdown>
  );
}

With AI SDK

'use client';

import { useChat } from '@ai-sdk/react';
import { useState } from 'react';
import { Streamdown } from 'streamdown';

export default function Page() {
  const { messages, sendMessage, status } = useChat();
  const [input, setInput] = useState('');

  return (
    <>
      {messages.map(message => (
        <div key={message.id}>
          {message.parts.filter(part => part.type === 'text').map((part, index) => (
            <Streamdown isAnimating={status === 'streaming'} key={index}>{part.text}</Streamdown>
          ))}
        </div>
      ))}

      <form
        onSubmit={e => {
          e.preventDefault();
          if (input.trim()) {
            sendMessage({ text: input });
            setInput('');
          }
        }}
      >
        <input
          value={input}
          onChange={e => setInput(e.target.value)}
          disabled={status !== 'ready'}
          placeholder="Say something..."
        />
        <button type="submit" disabled={status !== 'ready'}>
          Submit
        </button>
      </form>
    </>
  );
}

Customizing Plugins

When you need to override the default plugins (e.g., to configure security settings), you can import the default plugin configurations and selectively modify them:

import { Streamdown, defaultRehypePlugins } from 'streamdown';
import { harden } from 'rehype-harden';

export default function Page() {
  const markdown = `
[Safe link](https://example.com)
[Unsafe link](https://malicious-site.com)
  `;

  return (
    <Streamdown
      rehypePlugins={[
        defaultRehypePlugins.raw,
        defaultRehypePlugins.katex,
        [
          harden,
          {
            defaultOrigin: 'https://example.com',
            allowedLinkPrefixes: ['https://example.com'],
          },
        ],
      ]}
    >
      {markdown}
    </Streamdown>
  );
}

The defaultRehypePlugins and defaultRemarkPlugins exports provide access to:

defaultRehypePlugins:

• harden - Security hardening with rehype-harden (configured with wildcard permissions by default)
• raw - HTML support
• katex - Math rendering with KaTeX

defaultRemarkPlugins:

• gfm - GitHub Flavored Markdown support
• math - Math syntax support

Props

Streamdown accepts all the same props as react-markdown, plus additional streaming-specific options:

Prop	Type	Default	Description
children	string	-	The Markdown content to render
parseIncompleteMarkdown	boolean	true	Parse and style unterminated Markdown blocks
className	string	-	CSS class for the container
components	object	-	Custom component overrides
rehypePlugins	array	[[harden, { allowedImagePrefixes: ["*"], allowedLinkPrefixes: ["*"], defaultOrigin: undefined }], rehypeRaw, [rehypeKatex, { errorColor: "var(--color-muted-foreground)" }]]	Rehype plugins to use. Includes rehype-harden for security, rehype-raw for HTML support, and rehype-katex for math rendering by default
remarkPlugins	array	[[remarkGfm, {}], [remarkMath, { singleDollarTextMath: false }]]	Remark plugins to use. Includes GitHub Flavored Markdown and math support by default
shikiTheme	[BundledTheme, BundledTheme]	['github-light', 'github-dark']	The light and dark themes to use for code blocks
mermaidConfig	MermaidConfig	-	Custom configuration for Mermaid diagrams (theme, colors, etc.)
controls	boolean | { table?: boolean, code?: boolean, mermaid?: boolean }	true	Control visibility of copy/download buttons
isAnimating	boolean	false	Whether the component is currently animating. This is used to disable the copy and download buttons when the component is animating.

Architecture

Streamdown is built as a monorepo with:

• packages/streamdown - The core React component library
• apps/website - Documentation and demo site

Development

# Install dependencies
pnpm install

# Build the streamdown package
pnpm --filter streamdown build

# Run development server
pnpm dev

# Run tests
pnpm test

# Build packages
pnpm build

Requirements

• Node.js >= 18
• React >= 19.1.1

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.