cssnext has some features that LESS doesn't like auto prefixing CSS rules according to your browser scope. So it rely on caniuse database which is why it's not

cssnext has some features that LESS doesn't like auto prefixing CSS rules according to your browser scope. So it rely on caniuse database which is why it's not a good idea to use it on the client side. That being said, there is a playground so you can try it http://cssnext.io/playground/ http://cssnext.io/playground/ SourceMap is supported, see options http://cssnext.io/usage/#sourcemap http://cssnext.io/usage/#sourcemap