# html-to-markdown

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Elixir bindings for the Rust html-to-markdown engine. The package exposes a fast HTML to Markdown converter implemented with Rustler.
Ship identical Markdown across every runtime while enjoying native performance with Rustler NIF bindings.


## Installation

```bash
Add {:html_to_markdown, "~> 3.0"} to mix.exs deps
```



Requires Elixir 1.19+ and OTP 28. Add to your `mix.exs`:

```elixir
def deps do
  [
    {:html_to_markdown, "~> 3.0.0"}
  ]
end
```






## Performance Snapshot

Apple M4 • Real Wikipedia documents • `convert()` (Elixir)

| Document | Size | Ops/sec | Throughput |
| -------- | ---- | ------- | ---------- |
| Lists (Timeline) | 129KB | 2,547 | 321.7 MB/s |
| Tables (Countries) | 360KB | 835 | 293.8 MB/s |
| Medium (Python) | 656KB | 439 | 281.5 MB/s |
| Large (Rust) | 567KB | 485 | 268.7 MB/s |
| Small (Intro) | 463KB | 581 | 262.9 MB/s |




## Quick Start

Basic conversion:

```elixir
{:ok, result} = HtmlToMarkdown.convert("<h1>Hello</h1><p>This is <strong>fast</strong>!</p>")
IO.puts(result.content)
```



With conversion options:

```elixir
opts = %HtmlToMarkdown.Options{wrap: true, wrap_width: 40}
{:ok, result} = HtmlToMarkdown.convert("<h1>Hello</h1><p>World</p>", opts)
IO.puts(result.content)
```




## API Reference

### Core Function


**`HtmlToMarkdown.convert(html, options \\ nil) :: {:ok, ConversionResult.t()} | {:error, term()}`**

Converts HTML to Markdown. Returns `{:ok, result}` where result is a struct with all results in a single call.

```elixir
{:ok, result} = HtmlToMarkdown.convert(html)
result.content    # Converted Markdown string
result.metadata   # Metadata map (when extract_metadata: true)
result.tables     # Table data list (when extract_tables: true)
result.document   # Document-level info
result.images     # Extracted images
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](https://djot.net/), 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


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

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

# Djot output
{:ok, 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.


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

{:ok, 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


```elixir
html = "<h1>Article</h1><img src=\"test.jpg\" alt=\"test\">"
opts = %HtmlToMarkdown.Options{extract_metadata: true}
{:ok, result} = HtmlToMarkdown.convert(html, opts)

IO.puts(result.content)                           # Converted Markdown
IO.inspect(result.metadata["document"]["title"])  # Document title
IO.inspect(result.metadata["headers"])            # All h1-h6 elements
IO.inspect(result.metadata["links"])              # All hyperlinks
IO.inspect(result.metadata["images"])             # All images with alt text
IO.inspect(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


```elixir
defmodule MyVisitor do
  use HtmlToMarkdown.Visitor

  @impl true
  def handle_link(_ctx, href, text, _title) do
    # Rewrite CDN URLs
    href = if String.starts_with?(href, "https://old-cdn.com") do
      String.replace(href, "https://old-cdn.com", "https://new-cdn.com")
    else
      href
    end
    {:custom, "[#{text}](#{href})"}
  end

  @impl true
  def handle_image(_ctx, src, _alt, _title) do
    # Skip tracking pixels
    if String.contains?(src, "tracking"), do: :skip, else: :continue
  end
end

html = "<a href=\"https://old-cdn.com/file.pdf\">Download</a>"
opts = %HtmlToMarkdown.Options{visitor: MyVisitor}
{:ok, result} = HtmlToMarkdown.convert(html, opts)
result.content
```





## Examples


## Links

- **GitHub:** [github.com/kreuzberg-dev/html-to-markdown](https://github.com/kreuzberg-dev/html-to-markdown)

- **Hex.pm:** [hex.pm/packages/html_to_markdown](https://hex.pm/packages/html_to_markdown)

- **Kreuzberg Ecosystem:** [kreuzberg.dev](https://kreuzberg.dev)
- **Discord:** [discord.gg/pXxagNK2zN](https://discord.gg/pXxagNK2zN)

## Contributing

We welcome contributions! Please see our [Contributing Guide](https://github.com/kreuzberg-dev/html-to-markdown/blob/main/CONTRIBUTING.md) 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](https://github.com/kreuzberg-dev/html-to-markdown/blob/main/LICENSE).

## Support

If you find this library useful, consider [sponsoring the project](https://github.com/sponsors/kreuzberg-dev).

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

- **GitHub Issues:** [github.com/kreuzberg-dev/html-to-markdown/issues](https://github.com/kreuzberg-dev/html-to-markdown/issues)
- **Discussions:** [github.com/kreuzberg-dev/html-to-markdown/discussions](https://github.com/kreuzberg-dev/html-to-markdown/discussions)
- **Discord Community:** [discord.gg/pXxagNK2zN](https://discord.gg/pXxagNK2zN)