Autoprefixer is a PostCSS plugin which parses your CSS and adds vendor prefixes
You can also see which browsers you choose by filter string on browsersl.ist
Autoprefixer online — web repl for original Autoprefixer. It parses your CSS and adds vendor prefixes to CSS rules using values from Can I Use. It is recommended by Google and used by Twitter and Taobao.
The Autoprefixer uses data on the popularity of browsers and support for vendor prefixes by browsers. Based on this information, it arranges and deletes the prefixes. It can help you get prefixes for: animations, transition, transform, grid, flex, flexbox and others.
You can configure which browsers to generate prefixes for in the distribution. More details on the syntax are in the documentation. There is also a block in the FAQ.
The IE grid layout polyfill is enabled, which is not by default in autoprefixer.
To Andrey Sitnik, author of PostCSS, Autoprefixer, browserslist and other awesome tools.