postcss/autoprefixer

Autoprefixer is a tool for web developers that automatically rewrites CSS files to add the vendor prefixes browsers need, so you don't have to remember or maintain them yourself. CSS rules sometimes work only when written with a special prefix like -webkit- or -moz- for certain browsers, which prefixes are actually required changes over time as browsers update. Autoprefixer reads your CSS, looks up real-world support data from the Can I Use website, and inserts only the prefixes still needed for the browsers you want to target. Technically, Autoprefixer is a plugin for PostCSS, a JavaScript tool that parses CSS into a structured form, lets plugins transform it, and writes it back out. You hand it source like ::placeholder { color: gray, } and it produces the expanded form with ::-moz-placeholder added alongside. Which browsers count as "supported" is controlled through Browserslist, typically a .browserslistrc file or a browserslist key in package.json, with queries such as "> 5%", and the README recommends using that shared config rather than passing options directly. Autoprefixer does not polyfill behaviour, it only adds prefixes. It also includes an opt-in mode that can translate modern CSS Grid syntax into the older IE 10/11 grid syntax, with documented limitations and control comments to enable or disable transformations per file. You would use Autoprefixer when you want to write clean, modern CSS once and let the build pipeline keep cross-browser support correct. It plugs into common build tools and workflows including Gulp, Webpack, CSS-in-JS, a CLI, other preprocessors, GUI tools, plain JavaScript, and various text editors and IDEs.