Components

Streamdown allows you to replace any Markdown element with your own React component while maintaining all of Streamdown's functionality.

Basic Usage

Pass custom components using the components prop:

app/page.tsx

<Streamdown
  components={{
    h1: ({ children }) => (
      <h1 className="text-4xl font-bold text-blue-600">
        {children}
      </h1>
    ),
    h2: ({ children }) => (
      <h2 className="text-3xl font-semibold text-blue-500">
        {children}
      </h2>
    ),
    p: ({ children }) => (
      <p className="text-gray-700 leading-relaxed">
        {children}
      </p>
    ),
  }}
>
  {markdown}
</Streamdown>

Available Components

You can override any of the following standard HTML components:

Headings: h1, h2, h3, h4, h5, h6
Text: p, strong, em
Lists: ul, ol, li
Links: a
Code: code, pre
Quotes: blockquote
Tables: table, thead, tbody, tr, th, td
Media: img
Other: hr, sup, sub, section

Component Props

Custom components receive all the props that the default components would receive, including:

children - The content to render
className - CSS class names from the Markdown AST (if applicable)
node - The Markdown AST node (for advanced use cases)
Element-specific props (e.g., href for links, src for images)

Custom components fully replace the default implementations, including their built-in Tailwind styles. The className prop only contains classes from the Markdown AST (e.g., language-js on code elements) — it does not include the default styles that Streamdown normally applies.

If you need to preserve the default appearance, you must re-apply the styles yourself. See the Styling documentation for the default classes, or use CSS selectors with data-streamdown attributes instead of component overrides when you only need visual changes.

For example, the default h2 component applies mt-6 mb-2 font-semibold text-2xl. When you override it, those styles are lost unless you include them:

app/page.tsx

<Streamdown
  components={{
    // ❌ Loses default spacing and font styles
    h2: ({ children }) => (
      <h2 className="text-blue-500">{children}</h2>
    ),
    // ✅ Preserves default styles alongside custom ones
    h2: ({ children, className }) => (
      <h2 className={`mt-6 mb-2 font-semibold text-2xl text-blue-500 ${className ?? ''}`}>
        {children}
      </h2>
    ),
  }}
>
  {markdown}
</Streamdown>

Inline Code

When you override components.code, you replace the entire code rendering pipeline — inline code, block code with syntax highlighting, mermaid diagrams, and custom renderers. To customize only inline code without affecting block code, use the inlineCode virtual component:

app/page.tsx

<Streamdown
  components={{
    inlineCode: ({ children }) => (
      <code className="rounded bg-violet-100 px-1.5 py-0.5 text-violet-800 text-sm">
        {children}
      </code>
    ),
  }}
>
  {markdown}
</Streamdown>

Block code blocks, syntax highlighting, and mermaid diagrams continue to work normally. You can also combine inlineCode with a custom code component — inlineCode handles inline spans while code handles fenced code blocks:

app/page.tsx

<Streamdown
  components={{
    inlineCode: ({ children }) => (
      <code className="bg-violet-100 text-violet-800 rounded px-1 text-sm">
        {children}
      </code>
    ),
    code: MyCustomCodeBlock,
  }}
>
  {markdown}
</Streamdown>

Streaming State

When streaming markdown, custom components can detect if their code fence is still being streamed using the useIsCodeFenceIncomplete hook. This is useful for expensive-to-render components where you want to show a loading state until the code block is complete.

app/page.tsx

import { Streamdown, useIsCodeFenceIncomplete } from "streamdown";

const MyCodeBlock = ({ children }) => {
  const isIncomplete = useIsCodeFenceIncomplete();

  if (isIncomplete) {
    return <div className="animate-pulse bg-muted h-24 rounded" />;
  }

  return <pre><code>{children}</code></pre>;
};

export default function Page() {
  return (
    <Streamdown
      components={{ code: MyCodeBlock }}
      isAnimating={isStreaming}
    >
      {markdown}
    </Streamdown>
  );
}

The hook returns true when all of the following are true:

isAnimating={true} (streaming mode is active)
The component is in the last block being streamed
That block has an unclosed code fence (``` without a closing ```)

Once the code fence closes, the hook returns false and your component can render normally—even while the rest of the markdown continues streaming.

This is particularly useful for Mermaid diagrams and syntax highlighters where continuous re-rendering during streaming would cause performance issues.

app/page.tsx

<Streamdown
  components={{
    a: ({ href, children, ...props }) => (
      <a
        href={href}
        className="text-purple-600 hover:text-purple-800 underline"
        {...props}
      >
        {children}
      </a>
    ),
  }}
>
  {markdown}
</Streamdown>

Preserving Table Interactivity

When overriding the table component, the built-in copy and download buttons are lost because custom components fully replace default implementations. To restore them, import the table action components and include them in your custom table:

app/page.tsx

import {
  Streamdown,
  TableCopyDropdown,
  TableDownloadDropdown,
} from "streamdown";

<Streamdown
  components={{
    table: ({ children, className }) => (
      <div data-streamdown="table-wrapper">
        <div className="flex items-center justify-end gap-1">
          <TableCopyDropdown />
          <TableDownloadDropdown />
        </div>
        <MyCustomTable className={className}>{children}</MyCustomTable>
      </div>
    ),
  }}
>
  {markdown}
</Streamdown>

The data-streamdown="table-wrapper" attribute is required — the action components use .closest() to find this wrapper, then .querySelector("table") to locate the <table> element inside it. Your custom table component must render a <table> element as a descendant of the wrapper div.

A TableDownloadButton component is also available for rendering a single-format download button instead of a dropdown:

app/page.tsx

import { TableDownloadButton } from "streamdown";

<TableDownloadButton format="csv" />

Lower-level utilities

For fully custom implementations, use the extraction and conversion utilities directly:

app/page.tsx

import {
  extractTableDataFromElement,
  tableDataToCSV,
  tableDataToTSV,
  tableDataToMarkdown,
} from "streamdown";

// Extract structured data from a <table> DOM element
const data = extractTableDataFromElement(tableElement);

// Convert to various formats
const csv = tableDataToCSV(data);
const tsv = tableDataToTSV(data);
const markdown = tableDataToMarkdown(data);

Custom HTML Tags

You can render custom HTML tags from AI responses (like <source>, <mention>, etc.) using the allowedTags prop alongside components. This is useful when you instruct the AI to output structured data that renders as interactive components.

For example, you might add a system prompt:

When referencing a source, use: <source id="123">Source Title</source>

The AI then outputs markdown containing:

According to the documentation <source id="abc">Getting Started Guide</source>, you should...

Setup

Use the allowedTags prop to specify which custom tags and attributes to allow through sanitization, then map them to React components:

app/page.tsx

<Streamdown
  allowedTags={{
    source: ["id"],  // Allow <source> tag with id attribute
  }}
  components={{
    source: ({ id, children }) => (
      <button
        onClick={() => console.log(`Navigate to source: ${id}`)}
        className="text-blue-600 underline cursor-pointer"
      >
        {children}
      </button>
    ),
  }}
>
  {markdown}
</Streamdown>

Multiple Custom Tags

You can allow multiple custom tags:

app/page.tsx

<Streamdown
  allowedTags={{
    source: ["id"],
    mention: ["user_id", "type"],
    action: ["name", "payload"],
  }}
  components={{
    source: ({ id, children }) => (
      <SourceBadge sourceId={id as string}>{children}</SourceBadge>
    ),
    mention: ({ user_id, children }) => (
      <UserMention userId={user_id as string}>{children}</UserMention>
    ),
    action: ({ name, payload, children }) => (
      <ActionButton name={name as string} payload={payload as string}>
        {children}
      </ActionButton>
    ),
  }}
>
  {markdown}
</Streamdown>

Data Attributes

Use data* in the attributes array to allow all data-* attributes on a tag:

app/page.tsx

<Streamdown
  allowedTags={{
    widget: ["data*"],  // Allow all data-* attributes
  }}
  components={{
    widget: (props) => <Widget {...props} />,
  }}
>
  {markdown}
</Streamdown>

Important Notes

Without allowedTags, custom tags are stripped by the sanitizer (content is preserved, tags are removed)
Only attributes listed in allowedTags are preserved; unlisted attributes are stripped
The allowedTags prop only works with the default rehype plugins

If you provide custom rehypePlugins, you'll need to configure rehype-sanitize yourself to allow custom tags. See the Security documentation for details.

Plain text tag content

By default, children of custom HTML tags are parsed as markdown. This means underscores, asterisks, and other markdown metacharacters in tag content get formatted unexpectedly — for example, <mention>some_user_name</mention> renders with italicized text instead of a literal underscore.

Use the literalTagContent prop to treat the children of specific tags as plain text:

app/page.tsx

<Streamdown
  allowedTags={{
    mention: ["user_id"],
  }}
  literalTagContent={["mention"]}
  components={{
    mention: ({ user_id, children }) => (
      <span className="text-blue-600">@{children}</span>
    ),
  }}
>
  {markdown}
</Streamdown>

Tags listed in literalTagContent must also be listed in allowedTags. Otherwise the tag is stripped by the sanitizer before literal content handling applies.

Security Considerations

When allowing custom HTML tags:

Only whitelist tags you explicitly need
Only whitelist attributes you explicitly need
Validate attribute values in your component before using them
Never allow script, style, or event handler attributes (onclick, etc.)

See the Security documentation for more details on HTML handling.

Components

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