Koog is a mixed-code generation tool. It supports a choice of comment styles (C-style block comments by default), and assumes that code-generation directives are written in Racket. Koog provides a Racket API, a command-line interface, and editor integration for Emacs and Vim. The one novel feature it has (compared to existing mixed-code generators) is the option of only (re)generating individual code regions, which provides more control when used interactively in an editor.