Working with Markdown in Kotlin: Libraries and Parsers

Working with Markdown in Kotlin: Overview of Libraries and Tools

Markdown is a popular markup language for formatting text, widely used in documentation, README files, blogs, and content management systems. In the Kotlin ecosystem, there are several mature libraries that allow you to parse Markdown, convert it to HTML, and create custom extensions. In this article, we will look at three main approaches: using commonmark-java, flexmark-java, and the native library kmarkdown.

1. The commonmark-java Library

commonmark-java is the official Java implementation of the CommonMark specification, which works great in Kotlin. It offers a simple API, high performance, and strict adherence to the standard.

Installation

Add the dependency to build.gradle.kts:

implementation("org.commonmark:commonmark:0.21.0")

Usage Example

import org.commonmark.parser.Parserimport org.commonmark.renderer.html.HtmlRenderer

fun main() {    val parser = Parser.builder().build()    val document = parser.parse("**Hello**, this is *Markdown* in Kotlin!")    val renderer = HtmlRenderer.builder().build()    val html = renderer.render(document)    println(html)    // Output: <p><strong>Hello</strong>, this is <em>Markdown</em> in Kotlin!</p>}

The library supports all basic elements: headings, lists, links, images, code, and code blocks. To extend functionality, you can add additional modules, for example, commonmark-ext-gfm-tables for GitHub Flavored Markdown tables.

2. The flexmark-java Library

flexmark-java is a more powerful and flexible alternative. It supports CommonMark, GitHub Flavored Markdown (GFM), as well as many extensions: footnotes, anchors, emojis, mathematical formulas, and custom syntaxes.

Installation

implementation("com.vladsch.flexmark:flexmark-all:0.64.8")

Example with Extensions

import com.vladsch.flexmark.html.HtmlRendererimport com.vladsch.flexmark.parser.Parserimport com.vladsch.flexmark.ext.tables.TablesExtensionimport com.vladsch.flexmark.ext.gfm.strikethrough.StrikethroughExtension

fun main() {    val extensions = listOf(TablesExtension.create(), StrikethroughExtension.create())    val parser = Parser.builder().extensions(extensions).build()    val document = parser.parse("| Header | Description ||-----------|----------|| Kotlin    | Language     |

~~Strikethrough text~~")    val renderer = HtmlRenderer.builder().extensions(extensions).build()    println(renderer.render(document))}

Flexmark also allows you to customize rendering: add CSS classes, change attribute order, create custom visitors for the AST tree. This makes it an ideal choice for complex projects that require fine-grained output control.

3. The Native kmarkdown Library

kmarkdown is a pure Kotlin implementation of a Markdown parser, written using coroutines and built-in language features. It is lightweight and requires no additional dependencies beyond the Kotlin standard library.

Installation

implementation("net.nightwhistler:kmarkdown:1.0.2")

Example

import net.nightwhistler.kmarkdown.KMarkdown

fun main() {    val markdown = KMarkdown()    val html = markdown.parseToHtml("# Heading

Regular **text**")    println(html)    // Output: <h1>Heading</h1><p>Regular <strong>text</strong></p>}

Kmarkdown is suitable for simple scenarios where extended GFM features are not required. Its advantages are clean code and the absence of