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Fastest solution to spell check camel case code or plain text

  • Fast
  • Spell check camel case code without any extra setup
  • Support both Aspell and Hunspell
  • Powerful and easy to set up





Wucuo is uploaded to The best way to install is Emacs package manager.

If using GNU Guix, Wucuo and its dependencies can be installed via guix install emacs-guix.


Please install either Aspell or Hunspell and the dictionaries at first.

This program does not mess up your Flyspell configuration. It assumes Flyspell is already configured properly.

But if you get some problem on Flyspell configuration, check sample configuration in “Tips” section.


Add below code into ~/.emacs to enable wucuo,

(add-hook 'prog-mode-hook #'wucuo-start)
(add-hook 'text-mode-hook #'wucuo-start)

The spell checking starts when current buffer is saved.

See wucuo-check-nil-font-face on how to check plain text (text without font).

Please note Wucuo is a complete solution. You should turn off flyspell-prog-mode and flyspell-mode before using this program.

Wucuo uses Flyspell API. So the good news is your configuration for flyspell still works.

Flyspell provides two minor modes, flyspell-prog-mode and flyspell-mode. They also use Flyspell API.

This program replaces these two minor modes.


Configure Flyspell

Flyspell configuration is shared by flyspell-prog-mode, flyspell-mode, and wucuo.

Even you don’t use this program, you still need configure flyspell.

If your existing Flyspell configuration already works, you don’t need read this section.

This section is to help users who have problem to setup flyspell.

You could read my article What’s the best spell check setup in emacs and my stackexchange answers on flyspell to learn the Flyspell knowledge.

Aspell configuration sample

Please install command line program Aspell and insert below code into ~/.emacs,

(setq ispell-program-name "aspell")
;; You could add extra option "--camel-case" for camel case code spell checking if Aspell 0.60.8+ is installed
;; @see
(setq ispell-extra-args '("--sug-mode=ultra" "--lang=en_US" "--run-together" "--run-together-limit=16"))

hunspell configuration sample

Please install command line program hunspell and insert below code into ~/.emacs,

(setq ispell-program-name "hunspell")
;; reset the hunspell so it STOPS querying locale!
;; "en_US" is the key to lookup in `ispell-local-dictionary-alist`
(setq ispell-local-dictionary "en_US")
;; two dictionaries "en_US" and "zh_CN" are used. Feel free to remove "zh_CN"
;; If `ispell-local-dictionary-alist' is nil, `ispell-local-dictionary' is passed
;; to hunpsell cli program as dictionary.
(setq ispell-local-dictionary-alist
      '(("en_US" "[[:alpha:]]" "[^[:alpha:]]" "[']" nil ("-d" "en_US" "zh_CN") nil utf-8)))
;; new variable `ispell-hunspell-dictionary-alist' is defined in Emacs
;; If it's nil, Emacs tries to automatically set up the dictionaries.
(when (boundp 'ispell-hunspell-dictionary-alist)
      (setq ispell-hunspell-dictionary-alist ispell-local-dictionary-alist))

Spell check file and directory

The function wucuo-spell-check-file will spell check one file and report typos. The function wucuo-spell-check-directory will spell check files under one directory and report typos.

Above functions could be used through Emacs CLI.

Example to use aspell to syntax check all files under current directory,

emacs -batch -Q -L ~/projs/wucuo -l ~/projs/wucuo/wucuo.el --eval '(let ((ispell-program-name "aspell") (ispell-extra-args (wucuo-aspell-cli-args t))) (wucuo-spell-check-directory "."))'

Example to use hunspell to syntax check one file,

emacs -batch -Q -L ~/projs/wucuo -l ~/projs/wucuo/wucuo.el --eval '(let ((ispell-program-name "hunspell") (ispell-local-dictionary "en_US")) (wucuo-spell-check-file ""))'

Start mode

The default value of wucuo-flyspell-start-mode is “fast”.

If wucuo-flyspell-start-mode is “fast”, wucuo-start calls flyspell-region to check visible region in current window periodically.

If wucuo-flyspell-start-mode is “normal”, wucuo-start calls flyspell-buffer periodically.

The interval of buffer checking or region checking is controlled by wucuo-update-interval.

Wucuo only checks typo in current buffer or the visible region. So it’s much faster than flyspell-mode.

Skip spell checking under certain circumstances

You can define a function in wucuo-spell-check-buffer-predicate. If the function returns t, the spell checking of current buffer will continue. If it returns nil, the spell checking is skipped.

Here is sample to skip checking in specified major modes,

(setq wucuo-spell-check-buffer-predicate
      (lambda ()
        (not (memq major-mode

Change dictionaries

See wucuo-aspell-language-to-use and wucuo-hunspell-dictionary-base-name

Only check words with specified font faces

(setq wucuo-personal-font-faces-to-check '(font-lock-comment-face))

Flyspell wrongly mark some word as typo

There are two solutions.

Solution 1, set up Emacs with below code,

(defun my-checker (word)
  "If WORD is typo, return t."
  ;; add your own setup code here
(setq wucuo-extra-predicate #'my-checker)

Solution 2, create a personal dictionary

If you use Aspell, run M-x wucuo-create-aspell-personal-dictionary to create a plain text dictionary ~/.aspell.en.pws. The “en” in “.aspell.en.pws” means the personal dictionary is an English dictionary. It’s actually language code assigned to the English. Aspell’s option --lang uses same language code (“en” is default value).

If you use Hunspell, run M-x wucuo-create-hunspell-personal-dictionary to create a plain text dictionary ~/.hunspell_en_US. “en_US” is the language code used by Hunspell’s option -d.

Here is my ~/.aspell.en.pws.

Hunspell’s personal dictionary is in the same format as Aspell.

Please note it’s reported that the dictionary file should be utf-8 encoded.

Speed up checking if aspell is used

(setq ispell-extra-args "--run-together")

Ignore major mode’s own flyspell predicate

Or if you need replace the default configuration of multiple major modes, you can use below code,

(setq wucuo-modes-whose-predicate-ignored '("typescript-mode"))

Detect font face at point

Use wucuo-current-font-face to detect font face at point.

Skip spell checking when buffer or visible region is too big

In wucuo-flyspell-start-mode is “normal”, wucuo-spell-check-buffer-max specifies the maximum size of buffer to check.

In wucuo-flyspell-start-mode is “fast”, wucuo-spell-check-region-max specifies the maximum size of visible region to check.

Contact me

Report bug at


Fastest solution to spell check camel case code or plain text






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