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README.md

Xberg

html-to-markdown

High-performance HTML to Markdown converter with Java Panama FFI bindings to the Rust core. Uses Foreign Function & Memory API for zero-dependency, thread-safe conversion with full metadata extraction support.

What This Package Provides

  • Same renderer as every binding — output matches Rust, Python, Node.js, Ruby, PHP, Go, Java, .NET, Elixir, R, Dart, Swift, Zig, C FFI, and WASM.
  • Structured conversion result — Markdown plus metadata, links, headings, images, tables, and warnings where the binding exposes them.
  • Production defaults — HTML is parsed with the Rust core, sanitized by default, and rendered without runtime-specific Markdown drift.
  • Java package — Panama FFM binding for direct native calls without a sidecar process.

Installation

<dependency>
    <groupId>io.xberg</groupId>
    <artifactId>html-to-markdown</artifactId>
    <version>3.8.2</version>
</dependency>

Requires Java 25+ with Panama FFI support.

Maven:

<dependency>
    <groupId>io.xberg</groupId>
    <artifactId>html-to-markdown</artifactId>
    <version>3.8.2</version>
</dependency>

Gradle (Kotlin DSL):

implementation("io.xberg:html-to-markdown:3.8.2")

Performance Snapshot

Apple M4 · convert() · Real Wikipedia documents

Document Size Latency Throughput
Lists (Timeline) 129KB 291.5 MB/s
Tables (Countries) 360KB 272.0 MB/s
Mixed (Python) 656KB 258.5 MB/s

Quick Start

Basic conversion:

import io.xberg.htmltomarkdown.HtmlToMarkdown;
import io.xberg.htmltomarkdown.ConversionResult;

public class Example {
    public static void main(String[] args) {
        String html = "<h1>Hello World</h1><p>This is a <strong>test</strong>.</p>";
        ConversionResult result = HtmlToMarkdown.convert(html);
        System.out.println(result.content());
    }
}

With conversion options:

import io.xberg.htmltomarkdown.HtmlToMarkdown;
import io.xberg.htmltomarkdown.ConversionOptions;
import io.xberg.htmltomarkdown.ConversionResult;

public class MetadataExample {
    public static void main(String[] args) {
        String html = "<html><head><title>My Page</title></head>"
            + "<body><h1>Welcome</h1><a href=\"https://example.com\">Link</a></body></html>";

        ConversionOptions options = ConversionOptions.builder()
            .extractMetadata(true)
            .build();
        ConversionResult result = HtmlToMarkdown.convert(html, options);

        System.out.println("Markdown: " + result.content());
        System.out.println("Title: " + result.metadata().document().title());
        System.out.println("Headers: " + result.metadata().headers().size());
        System.out.println("Links: " + result.metadata().links().size());
    }
}

Architecture

The converter routes each input through one of three tiers based on a fast prescan of the byte stream:

  1. Tier-1 — single-pass byte scanner. Handles 110+ HTML tags directly. Bails on any construct it cannot prove byte-equivalent to Tier-2.
  2. Tier-2 — DOM walker. Picks up Tier-1 bails and inputs the classifier rejected up front.
  3. Tier-3 — standards-conformant parser. Engaged for malformed HTML requiring full HTML5 repair.

The dispatcher is invisible to the caller. Output is byte-identical across tiers — enforced by a 116-snapshot oracle.

Capabilities

  • 16 languages, one Rust core. Rust, Python, Node.js, WASM, Java, Go, C#, PHP, Ruby, Elixir, R, Dart, Kotlin (Android), Swift, Zig, C ABI.
  • CommonMark-compatible Markdown with GFM-style tables.
  • Djot output: set output_format = "djot" (see Djot Output Format section below).
  • Real-HTML robust: unclosed tags, CDATA, custom elements, malformed entities, nested tables, mixed encodings handled without losing content.
  • Metadata extraction, visitor API, inline images, configurable preprocessing presets.
  • Per-group regression gates in CI: every PR runs the bench harness against per-group thresholds.

API Reference

Core Function

HtmlToMarkdown.convert(String html) : ConversionResult HtmlToMarkdown.convert(String html, ConversionOptions options) : ConversionResult

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

ConversionResult result = HtmlToMarkdown.convert(html);
String   markdown = result.content();   // Converted Markdown string
HtmlMetadata metadata = result.metadata();
List<TableData> tables = result.tables();

Options

ConversionOptions – Key configuration fields:

  • heading_style: Heading format ("underlined" | "atx" | "atx_closed") — default: "atx"
  • 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: true
  • 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

import io.xberg.htmltomarkdown.HtmlToMarkdown;
import io.xberg.htmltomarkdown.ConversionOptions;
import io.xberg.htmltomarkdown.OutputFormat;

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

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

// Djot output
String djot = HtmlToMarkdown.convert(html,
    ConversionOptions.builder()
        .withOutputFormat(OutputFormat.Djot)
        .build()
).content();
// 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.

import io.xberg.htmltomarkdown.HtmlToMarkdown;
import io.xberg.htmltomarkdown.ConversionOptions;
import io.xberg.htmltomarkdown.OutputFormat;

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

String plain = HtmlToMarkdown.convert(html,
    ConversionOptions.builder()
        .withOutputFormat(OutputFormat.Plain)
        .build()
).content();
// Result: "Title\n\nThis is bold and italic text."

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

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

Examples

Links

Part of Xberg

  • Xberg — document intelligence: text, tables, metadata from 91+ formats with optional OCR.
  • Xberg Enterprise — managed extraction API with SDKs, dashboards, and observability.
  • crawlberg — web crawling and scraping with HTML→Markdown and headless-Chrome fallback.
  • html-to-markdown — fast, lossless HTML→Markdown engine.
  • liter-llm — universal LLM API client with native bindings for 14 languages and 143 providers.
  • tree-sitter-language-pack — tree-sitter grammars and code-intelligence primitives.
  • alef — the polyglot binding generator that produces every per-language binding across the 5 polyglot repos.

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. Copyright © Kreuzberg, Inc.

Support

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

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