Flymake is an emacs minor mode that runs a syntax check tool over source files as you write them, on the fly. Essentially it calls the compiler for the relevant language and then parses the warnings. Because this is so obviously useful, I have it turned on by default in .emacs: ; Highlight syntax errors (require 'flymake) (add-hook 'find-file-hook 'flymake-find-file-hook) Recall also that I use emacs to view page source in Epiphany.