A Svelte port of Streamdown by Vercel - an all in one markdown renderer, designed specifically for AI-powered streaming applications.
npm install svelte-streamdown
# or
pnpm add svelte-streamdown
# or
yarn add svelte-streamdownPerfect for AI-powered applications that need to stream and render markdown content safely and beautifully, with support for incomplete markdown blocks, security hardening, and rich features like code highlighting, math expressions, and interactive diagrams.
- Incomplete Markdown Parsing: Handles unterminated blocks gracefully
- Progressive Rendering: Perfect for streaming AI responses
- Real-time Updates: Optimized for dynamic content
- Smooth Animations: Animate tokens and blocks as they are streamed.
- Image Origin Control: Whitelist allowed image sources
- Link Safety: Control link destinations
- Every component customizable with Svelte snippets
- Granular theming system - customize every part of every component
- Override default styling and behavior for any markdown element
- Full control over rendering with type-safe props
- Seamless integration with your design system
Beautiful, responsive typography with built-in Tailwind CSS classes for headings, lists, code blocks, and more. Comes with a complete default theme that works out of the box.
Full support for
- Basic text marks: bold, italic,
code,Strikethrough -
Subscriptand ^Superscript^ - Links
- Headings (H1βH6)
- Blockquotes
- Github alert
- Ordered & unordered lists (including roman, alpha, nested)
- Task lists ([ ] and [x])
- Code blocks
- Mermaid diagrams
- Math
$expressions$ - Escaping currency symbols ($140)
- Complex tables
- Footnotes 1
- Inline citations [ref] [ref2]
- MDX components (embed custom Svelte components)
Note
π§ AI Prompting Tip: For best results, use our comprehensive prompt covering all supported markdown features.
- Syntax highlighting powered by Shiki
- Copy-to-clipboard functionality
- Support any Shiki themes
LaTeX math support through KaTeX:
- Perfect rendering for scientific content
- Inline math:
$E = mc^2$ - Block math:
- Render Mermaid diagrams from code blocks
- Incremental rendering during streaming content
- Pan and Zoom
- Full screen mode
Example:
graph TD
A[Start] --> B{Is it working?}
B -->|Yes| C[Great!]
B -->|No| D[Debug]
D --> B
C --> E[End]
sequenceDiagram
participant User
participant Frontend
participant API
participant Database
User->>Frontend: Submit form
Frontend->>API: POST /api/data
API->>Database: INSERT query
Database-->>API: Success
API-->>Frontend: 200 OK
Frontend-->>User: Show success message
pie title Project Time Allocation
"Development" : 45
"Testing" : 25
"Documentation" : 15
"Meetings" : 15
| H1 | H2 | H3 |
|---|---|---|
| This cell spans 3 columns |
| Header 1 | Header 2 | Header 3 |
|---|---|---|
| This cell spans 2 columns | Normal | |
| Normal | Normal | Normal |
| Header 1 | Header 2 |
|---|---|
| This cell spans | Cell A |
| two rows ^ | Cell B |
| Header 1 | Header 2 |
|---|---|
| Cell B | Cell A |
| --------------- | -------- |
| Footer |
| Left | Center | Right |
|---|---|---|
| A | B | C |
| Product Category ||| Sales Data Q1-Q4 2024 |||| | Product | Region || Q1 | Q2 | Q3 | Q4 |
| Name | Type | Area | Revenue | Revenue | Revenue | Revenue |
|---|---|---|---|---|---|---|
| Laptop Pro | Electronics | North America | $45,000 | $52,000 | $48,000 | |
| Laptop Pro ^ | ^ | Europe | $32,000 | $38,000 | $41,000 | $44,000 |
| Laptop Pro ^ | ^ | Asia | $28,000 | $35,000 | $42,000 | |
| Office Chair | Furniture | North America | $15,000 | $18,000 | $16,000 | $17,000 |
| Office Chair ^ | ^ | Europe | $12,000 | $14,000 | $15,000 | $16,000 |
| Wireless Mouse | Electronics | Global | $25,000 | $28,000 | ||
| ------------- | --------- | ------------ | --------- | --------- | --------- | --------- |
| Total Revenue | $152,000 | $185,000 | $187,000 | $205,000 |
- First item
- Second item
- Third item
a. First item
b. Second item
c. Third item
A. First item
B. Second item
C. Third item
i. First item
ii. Second item
iii. Third item
I. First item
II. Second item
III. Third item
-
First level (numeric) a. Second level (lowercase alpha) i. Third level (lowercase roman) - Fourth level (bullet) I. Fifth level (uppercase roman) A. Sixth level (uppercase alpha)
-
Back to the first level
- Uncompleted task
- Completed task
- Another uncompleted task
- Nested uncompleted subtask
- Nested completed subtask
Important
Native support for Github style Alert
: Topic 1 : Description 1
: **Topic 2** : *Description 2*
: Topic 3 : Description 3
: Topic 3 : Description 3
Streamdown supports inline citations that allow you to reference external sources and display them in interactive popovers. Citations work out-of-the-box with a simple object structure and support nested references like this [cloudflare.website, vercel] will render into [cloudflare.website, vercel]
To enable inline citations, pass a sources object as a prop to the Streamdown component.
<script>
import { Streamdown } from 'svelte-streamdown';
let content = `According to [smith2023], AI is advancing rapidly. See also [nested.subsection] for related work.`;
let sources = {
"smith2023": {
title: "AI Research Paper",
url: "https://example.com/paper",
content: "Detailed content of the citation..."
},
"nested": {
"subsection": {
title: "Nested Citation",
url: "https://example.com/nested"
}
}
};
</script>
<Streamdown {content} {sources} />Citations work with objects containing these properties:
title (or name or author): Display title for the citationurl (or href, url, link or source): Link to the sourcecontent (or text, summary or excerpt): Rich content to display in carousel mode
Streamdown offers two ways to display citations:
- List View: Shows all citations in a compact list format
- Carousel View (default): Step-through navigation for multiple citations with full content display
You can control the display mode using the inlineCitationsMode prop:
<!-- List view -->
<Streamdown {content} {sources} inlineCitationsMode="list" />
<!-- Carousel view (default) -->
<Streamdown {content} {sources} inlineCitationsMode="carousel" />Citations appear as clickable buttons that open popovers when clicked. The popover shows:
- Source title and URL (when available)
- Favicon from the source domain
- Rich content (in carousel mode)
- Navigation controls (in carousel mode for multiple citations)
If your citation data structure doesn't match the default format, you can customize how citations are rendered using inlineCitationPreview, inlineCitationContent or inlineCitationPopover snippets:
<Streamdown {content} {sources}>
{#snippet inlineCitationPreview({ token })}
<!-- Customize the clickable citation button -->
{token.keys[0]}
{/snippet}
{#snippet inlineCitationContent({ source, key, token })}
<!-- Customize content displayed in popover -->
<div class="custom-content">
<h4>{source.customTitle || key}</h4>
<p>{source.customDescription}</p>
</div>
{/snippet}
</Streamdown>These snippets allow you to:
inlineCitationPreview: Customize the content of the clickable button that appears in the textinlineCitationContent: Customize how individual citation content is displayed within popoversinlineCitationPopover: Completely customize the list of citations
This Svelte port maintains feature parity with the original Streamdown while adapting to Svelte's patterns:
| Aspect | Original (React) | Svelte Port |
|---|---|---|
| Framework | React | Svelte 5 |
| Component API | JSX Components | Svelte Snippets |
| Styling | Tailwind CSS | Tailwind CSS (compatible) |
| Context | React Context | Svelte Context |
| Build System | Vite/React | Vite/SvelteKit |
| TypeScript | Full TS support | Full TS support |
| Engine | Remark / Rehype + marked | marked only |
Note
Streamdown comes with built-in Tailwind CSS classes for beautiful default styling. To ensure all styles are included in your build, add the following to your app.css or main CSS file:
This setup is primarily necessary if you're using Tailwind CSS v4's new @source directive or if you have aggressive purging enabled in older versions. If you're using standard Tailwind CSS v3+ with default purging, Streamdown's styles should be automatically included when the component is imported and used in your application.
This ensures that all Streamdown's default styling is included in your Tailwind build process.
@import 'tailwindcss';
/* Add Streamdown styles to your Tailwind build */
@source "../node_modules/svelte-streamdown/**/*";Streamdown includes an animation system designed specifically for streaming AI content, providing smooth and engaging visual feedback as text appears on screen.
The animation system works by:
- Tokenization: Text is broken down into tokens (words or characters) based on your configuration
- Sequential Animation: Each token animates as it is received
- Block-level Animation: Entire blocks (paragraphs, headings, code blocks) animate as units
Choose from 4 distinct animation styles:
A clean fade-in effect where text smoothly appears from transparent to opaque.
Text starts slightly blurred and comes into focus while fading in, creating a smooth reveal effect.
Text slides up from below while fading in, creating a dynamic upward motion.
Text slides down from above while fading in, creating a dynamic downward motion.
Tip
For production applications where the LLM is not streaming (static content), disable animations entirely by setting animation.enabled = false to minimize DOM elements and improve performance.
If using AI SDK mind to smooth stream the content to using word-level tokenization to avoid partial words not being animated.
Warning
Character-level tokenization (tokenize: 'char') creates significantly more DOM elements than word-level tokenization. Use character tokenization sparingly and only when the typewriter effect is essential for your user experience.
<script>
import { Streamdown } from 'svelte-streamdown';
let content = `# Hello World
This is a **bold** text and this is *italic*.
\`\`\`javascript
console.log('Hello from Streamdown!');
\`\`\`
`;
</script>
<Streamdown {content} /><script>
import { Streamdown } from 'svelte-streamdown';
let content = `# Custom Components Example
This heading will use a custom component!`;
</script>
<Streamdown {content}>
{#snippet heading({ children })}
<h1 class="mb-4 text-4xl font-bold text-blue-600">
{@render children()}
</h1>
{/snippet}
</Streamdown><script>
import { Streamdown } from 'svelte-streamdown';
let markdown = `
[Safe Link](https://trusted-domain.com/page)`;
</script>
<Streamdown
{content}
allowedImagePrefixes={['https://trusted-domain.com']}
allowedLinkPrefixes={['https://trusted-domain.com']}
/>| Prop | Type | Default | Description |
|---|---|---|---|
content |
string |
- | Required. The markdown content to render |
sources |
Record<string, any> |
- | Citation data object for inline citations |
class |
string |
- | CSS class names for the wrapper element |
parseIncompleteMarkdown |
boolean |
true |
Parse and fix incomplete markdown syntax |
defaultOrigin |
string |
- | Default origin for relative URLs |
allowedLinkPrefixes |
string[] |
['*'] |
Allowed URL prefixes for links |
allowedImagePrefixes |
string[] |
['*'] |
Allowed URL prefixes for images |
skipHtml |
boolean |
- | Skip HTML parsing entirely |
unwrapDisallowed |
boolean |
- | Unwrap instead of removing disallowed elements |
urlTransform |
UrlTransform | null |
- | Custom URL transformation function |
theme |
DeepPartial<Theme> |
- | Custom theme overrides |
baseTheme |
'tailwind' | 'shadcn' |
'tailwind' |
Base theme to use before applying overrides |
mergeTheme |
boolean |
true |
Whether to merge theme with base theme |
shikiTheme |
BundledTheme |
'github-light' |
Code highlighting theme |
mermaidConfig |
MermaidConfig |
- | Mermaid diagram configuration |
katexConfig |
KatexOptions | ((inline: boolean) => KatexOptions) |
- | KaTeX math rendering options |
animation |
AnimationConfig |
- | Animation configuration for streaming content |
animation.enabled |
boolean |
false |
Enable/disable animations |
animation.type |
'fade' | 'blur' | 'typewriter' | 'slideUp' | 'slideDown' |
'blur' |
Animation style for text appearance |
animation.duration |
number |
500 |
Animation duration in milliseconds |
animation.timingFunction |
'ease' | 'ease-in' | 'ease-out' | 'ease-in-out' | 'linear' |
'ease-in' |
CSS timing function for animations |
animation.tokenize |
'word' | 'char' |
'word' |
Tokenization method for text animations |
animation.animateOnMount |
boolean |
false |
Run the token animation on mount or not, useful if you render the Streamdown component in the same time as the first token is receive from the LLM |
extensions |
Array<Extension> |
[] |
Custom marked tokenizers to render special markdown blocks or inline tokens |
mdxComponents |
Record<string, Component> |
{} |
Map of MDX component names to Svelte components (e.g., { Card, Button }) |
children |
Snippet<[{token:GenericToken, streamdown: StreamdownContext, children: Snippet |
undefined |
Snippet used to render elements not supported by Streamdown, custom extensions, and MDX components |
Text Elements: heading, p, strong, em, del
Links & Media: a, img
Lists: ul, ol, li
Code: code, codeSpan
Tables: table, thead, tbody, tr, th, td, tfoot
Special Content: blockquote, hr, alert, mermaid, math, footnoteRef, inlineCitation
MDX Components: Handled via a single mdx snippet that receives token, props, and children. Use token.tagName to differentiate between components.
Note: The above elements are supported by Streamdown and should be customized using individual props or the theme system. MDX components require the mdx snippet.
Streamdown comes with two built-in themes:
- Default Theme: The standard theme with gray-based colors
- Shadcn Theme: A theme that uses shadcn/ui design tokens for seamless integration with shadcn-based projects
Beyond custom snippets, Streamdown provides a granular theming system that lets you customize every part of every component without writing custom snippets. You can use the built-in themes (default and shadcn) or create completely custom themes using the mergeTheme utility.
Every component has multiple themeable parts. For example, the code component has:
code: {
base: 'bg-gray-100 rounded p-2 font-mono text-sm', // Main code block
container: 'my-4 w-full overflow-hidden rounded-xl border', // Wrapper container
header: 'flex items-center justify-between bg-gray-100/80', // Header with language
button: 'cursor-pointer p-1 text-gray-600 transition-all', // Copy button
language: 'ml-1 font-mono lowercase', // Language label
pre: 'overflow-x-auto font-mono p-0 bg-gray-100/40' // Pre element
}<script>
import { Streamdown } from 'svelte-streamdown';
let content = `# Custom Theme Example
\`\`\`javascript
console.log('Beautiful code blocks!');
\`\`\`
> This blockquote is also themed
| Header 1 | Header 2 |
|----------|----------|
| Cell 1 | Cell 2 |
`;
// Custom theme overrides
let customTheme = {
code: {
container: 'my-6 rounded-2xl border-2 border-purple-200 shadow-lg',
header: 'bg-purple-50 text-purple-700 font-medium',
button: 'text-purple-600 hover:text-purple-800 hover:bg-purple-100'
},
blockquote: {
base: 'border-l-8 border-purple-400 bg-purple-50 p-4 italic text-purple-800'
},
table: {
base: 'border-purple-200 shadow-md',
container: 'my-6 rounded-lg overflow-hidden'
},
th: {
base: 'bg-purple-100 px-6 py-3 text-purple-900 font-bold'
},
td: {
base: 'px-6 py-3 border-purple-100'
}
};
</script>
<Streamdown {content} theme={customTheme} />Each component supports multiple themeable parts:
Headings (h1-h6): base
Text Elements (p, strong, em, del): base
Lists (ul, ol, li): base
Links (a): base, blocked (for blocked/unsafe links)
Code (code): base, container, header, button, language, skeleton, pre
Inline Code (inlineCode): base
Images (img): container, base, downloadButton
Tables (table, thead, tbody, tr, th, td): base, container (table only)
Blockquotes (blockquote): base
Alerts (alert): base, title, icon, plus type-specific styles (note, tip, warning, caution, important)
Mermaid (mermaid): base, downloadButton
Math (math, inlineMath): base
Other (hr, sup, sub): base
Themes are intelligently merged using Tailwind's class merging utility, so you only need to override the specific parts you want to customize while keeping the default styling for everything else.
Streamdown supports MDX-style JSX components, allowing you to embed custom Svelte components directly in your markdown content.
<script>
import { Streamdown } from 'svelte-streamdown';
let content = `
# Using MDX Components
<Card title="Hello" count={42}>
This is **markdown content** inside a component!
</Card>
<Button label="Click me" active={true} />
`;
</script>
<Streamdown {content}>
{#snippet mdx({ token, props, children })}
{#if token.tagName === 'Card'}
<div class="rounded-lg border border-gray-200 p-4 shadow-sm">
<h3 class="text-xl font-bold">{props.title}</h3>
<p class="text-gray-600">Count: {props.count}</p>
<div class="mt-2">
{@render children()}
</div>
</div>
{:else if token.tagName === 'Button'}
<button class="rounded px-4 py-2 {props.active ? 'bg-blue-500 text-white' : 'bg-gray-200'}">
{props.label}
</button>
{:else}
{@render children()}
{/if}
{/snippet}
</Streamdown>Instead of using the mdx snippet with conditional logic, you can pass Svelte components directly using the mdxComponents prop:
<script>
import { Streamdown } from 'svelte-streamdown';
import Card from './Card.svelte';
import Button from './Button.svelte';
let content = `
# Using MDX Components
<Card title="Hello" count={42}>
This is **markdown content** inside a component!
</Card>
<Button label="Click me" active={true} />
`;
</script>
<Streamdown {content} mdxComponents={{ Card, Button }} />Your Svelte components (Card.svelte, Button.svelte) should accept props and a children snippet:
<!-- Card.svelte -->
<script>
let { title, count, children } = $props();
</script>
<div class="rounded-lg border border-gray-200 p-4 shadow-sm">
<h3 class="text-xl font-bold">{title}</h3>
<p class="text-gray-600">Count: {count}</p>
<div class="mt-2">
{@render children()}
</div>
</div><!-- Button.svelte -->
<script>
let { label, active } = $props();
</script>
<button class="rounded px-4 py-2 {active ? 'bg-blue-500 text-white' : 'bg-gray-200'}">
{label}
</button>This approach is cleaner when you have standalone component files, while the mdx snippet approach is better for inline component definitions or when you need shared logic across components.
Self-closing components:
<Component attr="value" count={42} enabled={true} />Components with markdown children:
<Component title="Hello">
# This is a heading
This **markdown** content will be parsed!
</Component>MDX components support three attribute value types:
- Strings:
attr="hello"β"hello" - Numbers:
count={42}orvalue={3.14}β42,3.14 - Booleans:
active={true}ordisabled={false}βtrue,false - Expressions:
value={variableName}β"variableName"(stored as string)
- Component names must start with a capital letter (PascalCase)
- Valid:
<Card />,<MyComponent />,<Component123 /> - Invalid:
<card />,<myComponent />(these are treated as HTML)
MDX components are streaming-safe. Incomplete components are automatically handled during AI streaming:
- Incomplete tags like
<Component attrnot rendered to prevent runtime errors - Unclosed components like
<Card>contentare auto-closed with</Card> - Malformed attributes are escaped to prevent rendering errors
This ensures your UI remains stable even when receiving partial markdown from streaming AI responses.
The mdx snippet receives three parameters:
token: The full MdxToken withtagName,attributes,selfClosing, etc.props: Object containing all parsed attributes (e.g.,props.title,props.count)children: Snippet containing parsed markdown content
Use token.tagName to determine which component is being rendered:
<!-- Markdown: <Card title="Hello" count={5}>Content</Card> -->
<Streamdown {content}>
{#snippet mdx({ token, props, children })}
{#if token.tagName === 'Card'}
<div>
<h3>{props.title}</h3>
<span>Count: {props.count}</span>
{@render children()}
</div>
{:else if token.tagName === 'Alert'}
<div class="alert alert-{props.type}">
{@render children()}
</div>
{:else}
<!-- Fallback for unknown components -->
{@render children()}
{/if}
{/snippet}
</Streamdown>Streamdown is extensible through the use of custom extensions.
An extension is an object that has a name, a level and a tokenizer function.
name: The name of the extensionlevel: The level of the extension, can beblockorinlinetokenizer: The tokenizer function, see marked for more information
To render the extension custom tokens, you can then simply use the children snippet.
<script lang="ts">
import { Streamdown, type Extension } from 'svelte-streamdown';
const markedCollapsible: Extension = {
name: 'collapsible',
level: 'block',
tokenizer(this, src) {
// Match [detail]...[detail] blocks (case insensitive)
const detailMatch = src.match(/^\[detail\](.*?)\[detail\]/is);
if (detailMatch) {
const content = detailMatch[1] || '';
const tokens = this.lexer.blockTokens(content);
return {
type: 'detail',
raw: detailMatch[0], // The entire matched string including tags
tokens
};
}
return undefined;
}
};
</script>
<Streamdown
extensions={[markedCollapsible]}
content={`
[detail]
This is a collapsible **section**
[detail]`}
>
{#snippet children({ token, streamdown, children })}
{#if token.type === 'detail'}
<details>
<summary> Detail </summary>
<div>
{@render children()}
</div>
</details>
{/if}
{/snippet}
</Streamdown># Clone the repository
git clone <repository-url>
cd svelte-streamdown
# Install dependencies
pnpm install
# Start development server
pnpm dev
# Run tests
pnpm test
# Build for production
pnpm build# Build the library
pnpm build
# Preview the showcase app
pnpm previewContributions are welcome! This is a port of the original Streamdown project, so please:
- Check the original Streamdown repository for upstream changes
- Ensure compatibility with the original API
- Maintain feature parity where possible
- Add tests for new features if you want
MIT
- Original Streamdown: Vercel for creating the original React component
- Svelte Community: For the amazing framework that made this port possible
- All Contributors: For helping improve and maintain this project
Made with β€οΈ and π€
Footnotes
-
Reference render in a popover by default. with rich content support and multiline β©