cmark

cmark is the reference implementation of the CommonMark specification, written in the C programming language. It provides a Markdown parser that reads text, constructs an abstract syntax tree (AST), and can render the document to HTML. The library is designed to be small, portable, and straightforward to integrate into other software.

The API exposes a C interface for parsing Markdown into an AST and for rendering that AST to HTML. It includes utilities for traversing and inspecting the tree and a small command-line tool that converts Markdown input to HTML, useful for testing and scripting.

cmark is open-source and released under the BSD 3-Clause license. It was authored by John MacFarlane and is maintained by the CommonMark community. The project emphasizes faithful adherence to the CommonMark specification and provides a reliable baseline for compatibility testing.

Ecosystem and usage: as the standard reference implementation, cmark is widely used as a building block in software requiring a standards-compliant Markdown parser. A related project, cmark-gfm, extends the core with GitHub Flavored Markdown features. The core library is portable and has bindings and ports to multiple languages for broader adoption.