Flycheck — Syntax checking for GNU Emacs¶ Flycheck is a modern on-the-fly syntax checking extension for GNU Emacs, intended as replacement for the older Flymake extension which is part of GNU Emacs. For a detailed comparison to Flymake see Flycheck versus Flymake. It uses various syntax checking and linting tools to automatically check the contents of buffers while you type, and reports warnings a