postcss-syntax is a PostCSS plugin that automatically switches the syntax parser based on file extensions, eliminating the need to manually configure syntax for different file types. It supports CSS, SCSS, SASS, LESS, SugarSS, HTML, Markdown, and JSX, making it ideal for developers working with diverse file formats in PostCSS workflows. The plugin is particularly useful for build tools and task runners that process multiple stylesheet languages or mixed-content files.