flyspell

Flyspell is an on-the-fly spell checker for the GNU Emacs text editor. Implemented in Emacs Lisp, it performs spelling checks as you type and on demand, using an external spell checker such as ispell, aspell, or hunspell. Misspelled words are highlighted in the buffer, and suggested corrections can be offered.

Flyspell maintains a standard dictionary and a personal dictionary. It supports multiple languages and can be configured to use different dictionaries in different buffers. There are two common modes: flyspell-mode for ordinary text in any major mode, and flyspell-prog-mode for source code, where spelling checks focus on comments and strings.

Common commands include enabling or disabling the feature with M-x flyspell-mode, checking the entire buffer with M-x flyspell-buffer, and checking the word at point with M-x flyspell-word. Corrections can be chosen from a pop-up or minibuffer, and the mechanism can operate in idle time to reduce interruptions.

Configuration and availability: Flyspell relies on an external program (ispell, aspell, or hunspell), set via ispell-program-name. Dictionaries are configurable through variables such as ispell-dictionary and ispell-personal-dictionary. It is commonly included with Emacs or available from package repositories for other setups.