css-tree
A tool set for CSS: fast detailed parser (CSS → AST), walker (AST traversal), generator (AST → CSS) and lexer (validation and matching) based on specs and browser implementations
snapdragon
Easy-to-use plugin system for creating powerful, fast and versatile parsers and compilers, with built-in source-map support.
micromark
small commonmark compliant markdown parser with positional info and concrete tokens
json3
A JSON polyfill for older JavaScript platforms.