CartoCSS (short: Carto) is a language for map design. It is similar in syntax to CSS, but builds upon it with specific abilities to filter map data and by providing things like variables. It targets the Mapnik renderer and is able to generate Mapnik XML or a JSON variant of Mapnik XML. It can run from the command line or in the browser by using a bundler like Browserify.

Carto is an evolution of the Cascadenik idea and language, with an emphasis on speed and flexibility.