html-to-markdown

Rust Python Node.js WASM Java Go C# PHP Ruby Elixir R C Documentation License

html-to-markdown

Discord

Blazing-fast HTML to Markdown conversion for Ruby, powered by the same Rust engine used by our Python, Node.js, WebAssembly, and PHP packages. Ship identical Markdown across every runtime while enjoying native extension performance with Magnus bindings.

Installation

gem install html-to-markdown

Requires Ruby 3.2+ with Magnus native extension bindings. Published for Linux, macOS.

Performance Snapshot

Apple M4 · convert() · Real Wikipedia documents

Document Size Latency Throughput
Lists (Timeline) 129KB 0.71ms 182 MB/s
Tables (Countries) 360KB 2.15ms 167 MB/s
Mixed (Python wiki) 656KB 4.89ms 134 MB/s

Quick Start

Basic conversion:

require 'html_to_markdown'

html = "<h1>Hello</h1><p>This is <strong>fast</strong>!</p>"
result = HtmlToMarkdown.convert(html)
markdown = result[:content]

With conversion options:

require 'html_to_markdown'

html = "<h1>Hello</h1><p>This is <strong>fast</strong>!</p>"
result = HtmlToMarkdown.convert(html, heading_style: :atx, code_block_style: :fenced)
markdown = result[:content]

API Reference

Core Function

convert(html, options: nil, visitor: nil) -> ConversionResult

Converts HTML to Markdown. Returns a ConversionResult hash with all results in a single call.

require 'html_to_markdown'

result = HtmlToMarkdown.convert(html)
markdown = result[:content]       # Converted Markdown string
metadata = result[:metadata]      # Metadata (when extract_metadata: true)
tables   = result[:tables]        # Structured table data (when extract_tables: true)
document = result[:document]      # Document-level info
images   = result[:images]        # Extracted images
warnings = result[:warnings]      # Any conversion warnings

Options

ConversionOptions – Key configuration fields:

  • heading_style: Heading format ("underlined" | "atx" | "atx_closed") — default: "underlined"
  • list_indent_width: Spaces per indent level — default: 2
  • bullets: Bullet characters cycle — default: "*+-"
  • wrap: Enable text wrapping — default: false
  • wrap_width: Wrap at column — default: 80
  • code_language: Default fenced code block language — default: none
  • extract_metadata: Enable metadata extraction into result.metadata — default: false
  • extract_tables: Enable structured table extraction into result.tables — default: false
  • output_format: Output markup format ("markdown" | "djot" | "plain") — default: "markdown"

Djot Output Format

The library supports converting HTML to Djot, a lightweight markup language similar to Markdown but with a different syntax for some elements. Set output_format to "djot" to use this format.

Syntax Differences

Element Markdown Djot
Strong **text** *text*
Emphasis *text* _text_
Strikethrough ~~text~~ {-text-}
Inserted/Added N/A {+text+}
Highlighted N/A {=text=}
Subscript N/A ~text~
Superscript N/A ^text^

Example Usage

require 'html_to_markdown'

html = "<p>This is <strong>bold</strong> and <em>italic</em> text.</p>"

# Default Markdown output
markdown = HtmlToMarkdown.convert(html)
# Result: "This is **bold** and *italic* text."

# Djot output
djot = HtmlToMarkdown.convert(html, output_format: 'djot')
# Result: "This is *bold* and _italic_ text."

Djot's extended syntax allows you to express more semantic meaning in lightweight text, making it useful for documents that require strikethrough, insertion tracking, or mathematical notation.

Plain Text Output

Set output_format to "plain" to strip all markup and return only visible text. This bypasses the Markdown conversion pipeline entirely for maximum speed.

require 'html_to_markdown'

html = "<h1>Title</h1><p>This is <strong>bold</strong> and <em>italic</em> text.</p>"

plain = HtmlToMarkdown.convert(html, output_format: 'plain')
# Result: "Title\n\nThis is bold and italic text."

Plain text mode is useful for search indexing, text extraction, and feeding content to LLMs.

Metadata Extraction

The metadata extraction feature enables comprehensive document analysis during conversion. Extract document properties, headers, links, images, and structured data in a single pass — all via the standard convert() function.

Use Cases:

  • SEO analysis – Extract title, description, Open Graph tags, Twitter cards
  • Table of contents generation – Build structured outlines from heading hierarchy
  • Content migration – Document all external links and resources
  • Accessibility audits – Check for images without alt text, empty links, invalid heading hierarchy
  • Link validation – Classify and validate anchor, internal, external, email, and phone links

Zero Overhead When Disabled: Metadata extraction adds negligible overhead and happens during the HTML parsing pass. Pass extract_metadata: true in ConversionOptions to enable it; the result is available at result.metadata.

Example: Quick Start

require 'html_to_markdown'

html = '<h1>Article</h1><img src="test.jpg" alt="test">'
result = HtmlToMarkdown.convert(html, extract_metadata: true)

puts result[:content]                             # Converted Markdown
puts result[:metadata][:document][:title]         # Document title
puts result[:metadata][:headers]                  # All h1-h6 elements
puts result[:metadata][:links]                    # All hyperlinks
puts result[:metadata][:images]                   # All images with alt text
puts result[:metadata][:structured_data]          # JSON-LD, Microdata, RDFa

Visitor Pattern

The visitor pattern enables custom HTML→Markdown conversion logic by providing callbacks for specific HTML elements during traversal. Pass a visitor as the third argument to convert().

Use Cases:

  • Custom Markdown dialects – Convert to Obsidian, Notion, or other flavors
  • Content filtering – Remove tracking pixels, ads, or unwanted elements
  • URL rewriting – Rewrite CDN URLs, add query parameters, validate links
  • Accessibility validation – Check alt text, heading hierarchy, link text
  • Analytics – Track element usage, link destinations, image sources

Supported Visitor Methods: 40+ callbacks for text, inline elements, links, images, headings, lists, blocks, and tables.

Example: Quick Start

require 'html_to_markdown'

class MyVisitor
  def visit_link(ctx, href, text, title = nil)
    # Rewrite CDN URLs
    if href.start_with?('https://old-cdn.com')
      href = href.sub('https://old-cdn.com', 'https://new-cdn.com')
    end
    { type: :custom, output: "[#{text}](#{href})" }
  end

  def visit_image(ctx, src, alt = nil, title = nil)
    # Skip tracking pixels
    src.include?('tracking') ? { type: :skip } : { type: :continue }
  end
end

html = '<a href="https://old-cdn.com/file.pdf">Download</a>'
result = HtmlToMarkdown.convert(html, visitor: MyVisitor.new)
markdown = result[:content]

Examples

Contributing

We welcome contributions! Please see our Contributing Guide for details on:

  • Setting up the development environment
  • Running tests locally
  • Submitting pull requests
  • Reporting issues

All contributions must follow our code quality standards (enforced via pre-commit hooks):

  • Proper test coverage (Rust 95%+, language bindings 80%+)
  • Formatting and linting checks
  • Documentation for public APIs

License

MIT License – see LICENSE.

Support

If you find this library useful, consider sponsoring the project.

Have questions or run into issues? We're here to help: