Streamdown Release Notes

Minor Changes

• d6666b6: Add lineNumbers prop to disable line numbers in code blocks

• d4ec6c0: Add meta prop to CustomRendererProps. Custom renderers now receive the raw metastring from the code fence (everything after the language identifier, e.g. ```rust {1} title="foo" → meta = '{1} title="foo"'). The prop is optional (meta?: string) and is undefined when no metastring is present. Existing custom renderers are unaffected.

Patch Changes

• ac8d839: Add staggered animation-delay to streaming word/character animations so new content cascades in sequentially instead of all animating simultaneously. Configurable via the new stagger option (default 40ms). Set stagger: 0 to restore the previous behavior.

• add5374: Enable horizontal scrolling on code blocks so long lines are accessible instead of being clipped by overflow-hidden.

• 75845c0: Fix unnecessary re-renders of code blocks during streaming updates.

• Problem: In streaming mode, when new content arrives (e.g. a paragraph is appended), completed code blocks that haven't changed were still re-rendering. This happened because the Streamdown component used inline object literals as default parameter values for linkSafety ({ enabled: true }). Every time children changed and Streamdown re-rendered, these inline defaults created new references, which caused the contextValue useMemo to recompute a new StreamdownContext object. Since React propagates context changes through memo boundaries, any context consumer inside a memoized Block (such as CodeBlock) would re-render even though the block's own props were unchanged.

• Fix: Extract the inline default values for linkSafety into module-level constants (defaultLinkSafetyConfig). This ensures referential stability across renders, so contextValue only recomputes when the actual values change — not just because children updated.

• 8b1c262: fix: prepend UTF-8 BOM to CSV downloads for Excel compatibility
  save() now prepends \uFEFF for text/csv string content so Excel on
  Windows detects UTF-8 encoding instead of falling back to ANSI.

• TableDownloadButton refactored to use save() instead of inline Blob
  creation, ensuring the public API also gets the BOM fix.

• b105c64: Fix custom tag content being prematurely split when content follows the opening tag on the same line and contains double newlines (\n\n). The preprocessor now ensures proper HTML block structure so the parser treats the entire tag as a single unit.

• 9e6f991: Increase dropdown z-index for table copy and download menus to prevent clipping by surrounding elements.

• 9c18748: docs: document required CSS custom properties (shadcn/ui design tokens) in README

• 7b62e9a: Replace Tailwind v4-only :last: and :first: variant syntax with [&>:last-child]: and [&>:first-child]: arbitrary variants for compatibility with both Tailwind CSS v3 and v4. Fixes caret rendering on every line instead of only the last child in v3.

• Updated dependencies [e50b0c4]

• Updated dependencies [716a5f0]

• [email protected]

Minor Changes

• e50b0c4: Add opt-in inline KaTeX completion ($formula → $formula$) via a new inlineKatex option that defaults to false to avoid ambiguity with currency symbols. Also fixes block KaTeX completion when streaming produces a partial closing $.

• 716a5f0: Escape single ~ between word characters to prevent false strikethrough rendering (e.g. 20~25°C no longer renders as strikethrough). Adds a new singleTilde option (enabled by default) that can be disabled via { singleTilde: false }.

Minor Changes

• 5edff75: Clarified Tailwind @source configuration for Streamdown and optional plugins.
  Updated documentation to keep the global @source for core streamdown only, move plugin @source guidance to plugin docs with examples, and add a caveat to include plugin entries only if installed.
• 57cd3b5: Add support for custom starting line numbers in code blocks via the startLine meta option.
  Code blocks can now specify a starting line number in the meta string:

  const x = 1;
  

  This renders line numbers beginning at 10 instead of the default 1. The feature works by parsing the startLine=N value from the fenced-code meta string and applying counter-reset: line N-1 to the <code> element.
• 57cd3b5: Add support for customizing icons via the icons prop on <Streamdown>.
  Users can override any subset of the built-in icons (copy, download, zoom, etc.) by passing a Partial<IconMap>:
  import { Streamdown, type IconMap } from "streamdown";
  <Streamdown icons={{ CheckIcon: MyCheckIcon }}>{content}</Streamdown>;
  Unspecified icons fall back to defaults.
• 01d27e9: Add support for custom Shiki themes via a themes option on createCodePlugin, accepting a [light, dark] pair of bundled theme names or full theme registration objects.
• 2cf559d: Add a virtual inlineCode key to the components prop, allowing inline code spans to be styled independently from fenced code blocks without manually detecting block vs. inline context.
• 27c7b03: Export table action components (TableCopyDropdown, TableDownloadButton, TableDownloadDropdown) and utilities (extractTableDataFromElement, tableDataToCSV, tableDataToTSV, tableDataToMarkdown, escapeMarkdownTableCell, TableData), enabling custom table overrides to preserve copy/download interactivity.
• fb76275: Add a fullscreen overlay for tables with Escape/backdrop-click to close and scroll locking, controlled via controls.table.fullscreen. Copy and download controls remain available in the fullscreen view.
• b392fbe: Add literalTagContent prop that accepts an array of custom HTML tag names (e.g. ['mention']) whose children should be treated as plain text, escaping markdown metacharacters so user-supplied labels aren't interpreted as formatting.
• c4c86fa: Add a dir prop that accepts "ltr", "rtl", or "auto". When set to "auto", each block's text direction is detected by scanning for the first strong Unicode character (Arabic, Hebrew, Thaana, etc.).
• 00872f0: Add a prefix prop that prepends a namespace to all generated Tailwind utility classes (e.g. flex becomes tw:flex), enabling Tailwind v4's prefix() feature for projects that need to avoid class name collisions.
• 401b901: Add support for custom renderers via plugins.renderers, allowing fenced code blocks with specific languages to be rendered by a custom component instead of the default CodeBlock.

Patch Changes

• f398611: Add onAnimationStart and onAnimationEnd callback props that fire when streaming animation begins and completes, useful for coordinating UI state with the animation lifecycle.
• f2a7e51: Fix empty lines in syntax-highlighted code blocks collapsing into nothing by rendering a newline character for empty token rows, preserving whitespace when copying.
• 9ba8511: fix: prevent ordered list animation retrigger during streaming
  When streaming content contains multiple ordered (or unordered) lists,
  the Marked lexer merges them into a single block. As each new item appears
  the block is re-processed through the rehype pipeline, re-creating all
  data-sd-animate spans. This caused already-visible characters to re-run
  their CSS entry animation.
  Two changes address the root cause:
  Per-block prevContentLength tracking – each Block component
  now keeps a useRef with the content length from its previous render.
  Before each render the animatePlugin.setPrevContentLength(n) method is
  called so the rehype plugin can detect which text-node positions were
  already rendered. Characters whose cumulative hast-text offset falls below
  the previous raw-content length receive --sd-duration:0ms, making them
  appear in their final state instantly rather than re-animating.
  Stable animatePlugin reference – the animatePlugin useMemo
  now uses value-based dependency comparison instead of reference equality
  for the animated option object. This prevents the plugin from being
  recreated on every parent re-render when the user passes an inline object
  literal (e.g. animated={{ animation: 'fadeIn' }}). A stable reference
  is required because the rehype processor cache uses the function name as
  its key and always returns the first cached closure; only the original
  config object is ever read by the processor.
• 781178b: Add a granular controls prop that accepts a boolean to toggle all controls or an object with per-feature flags (code, table, mermaid) for fine-grained control over copy, download, fullscreen, and pan/zoom buttons.
• e129f09: Add a translations prop for overriding all user-facing UI strings (copy/download button labels, modal text, image alt text, etc.), enabling full i18n support.
• Updated dependencies [a725579]
• [email protected]

Minor Changes

• 3657e42: Add useIsCodeFenceIncomplete hook for detecting incomplete code fences during streaming
  Custom components can now detect when the code fence in their block is still being streamed. This is useful for deferring expensive renders (syntax highlighting, Mermaid diagrams) until the code block is complete.

  import { useIsCodeFenceIncomplete } from "streamdown";
  const MyCodeBlock = ({ children }) => {
    const isIncomplete = useIsCodeFenceIncomplete();
    if (isIncomplete) {
      return <div>Loading code...</div>;
    }
    return (
      <pre>
        <code>{children}</code>
      </pre>
    );
  };
  

  The hook returns true when:

  • Streaming is active (isAnimating={true})
  • The component is in the last block being streamed
  • That block has an unclosed code fence
    The default code block component now uses this hook to set a data-incomplete attribute when incomplete, enabling CSS-based loading states.

• 32fb079: fix: hide download button on broken images and display a custom "Image not available" message instead

• d73d7bb: Make the action buttons in code block header sticky.
  Ensures copy buttons remain accessible for long code blocks.
  Improves usability when viewing large snippets.

• 15645da: Move code block lazy loading to the highlighting layer so block shells render immediately with plain text content before syntax colors resolve. This improves visual stability and removes the spinner fallback for standard code blocks.

Patch Changes

• 0987479: fix: codeblock highlight flicker while streaming
• 5d438ca: Add support for copying table data as Markdown in TableCopyDropdown.
  Introduces a Markdown copy option alongside existing formats.
  Allows users to quickly copy tables in valid Markdown format.
• ce9b4c2: Fix syntax highlighting
• ba03332: Redesign Mermaid diagram
• 6e91867: fix nested same-tag HTML block parsing in parseMarkdownIntoBlocks
• 7f9127b: Add normalizeHtmlIndentation prop to prevent indented HTML tags from being treated as code blocks
• fdef60d: Bump rehype-harden to fix "can't access property "type", node is undefined"
• 1abbf1e: Redesign table
• fb9f97c: handle custom tags with blank lines in content

Updated dependencies [6374fbf]
[email protected]