Format-all is a simple yet awesome Emacs package that allows you to “format source code in different programming languages using the same command, instead of learning a different Emacs package and formatting command for each language” (Reference). The author chose great default formatters for each programming language, so the package is almost plug-and-play. For instance, format-all uses clang-format for C/C++, prettier for JavaScript/Typescript, and black or yapf for Python. You can find the list of supported languages here. On top of that, format-all provides an Emacs minor mode, format-all-mode, that enables format on save. Like most third-party Emacs packages, it’s recommended to install format-all from MELPA.
After installation, there’s little configuration to be done. You have to make sure that you have the external formatter programs (e.g. clang-format, prettier, etc.) installed and put on your PATH. I define a custom function to extend the format-all-buffer command to operate on Prolog buffers as well, since format-all currently does not support the Prolog language. With inspiration taken from Visual Studio Code, I bind Alt-Shift-f to invoke my custom function and auto-format the current buffer. Lastly, I make sure the default formatter is used whenever I enter a coding buffer of a recognized programming language.
Putting everything together, this is all the configuration I have for format-all:
1
2
3
4
5
6
7
8
9
10
11
(use-package format-all
:preface
(defun ian/format-code ()
"Auto-format whole buffer."
(interactive)
(if (derived-mode-p 'prolog-mode)
(prolog-indent-buffer)
(format-all-buffer)))
:config
(global-set-key (kbd "M-F") #'ian/format-code)
(add-hook 'prog-mode-hook #'format-all-ensure-formatter))
Here, M-F is synonymous with Alt-Shift-f because Emacs understands Alt as the Meta key. I didn’t enable “format-on-save” because I’m more used to manually invoking the formatting function.
If you’re interested in more customization options for format-all, such as setting specific formatters for a project (via .dir-locals.el), you can read this section of the README. If you are unfamiliar with use-package, you can read my quick-start guide here.
That’s all for today, have a good one.
Update (Apr 2026)
When I wrote this post back in 2021, I was in university writing predominantly personal projects where I controlled the style of the entire codebase. A few years into working professionally as a software engineer, I’ve found myself reaching for format-all-region far more often than format-all-buffer. Most days I’m working on shared codebases and only want to format the new code I’m adding - formatting an entire file touched by other authors generates whitespace noise in my commits and is frowned upon in most engineering teams.
The format-all package has since implemented the very handy format-all-region-or-buffer command that will intelligently call either format-all-region or format-all-buffer depending on whether a region is active. In addition, format-all also supports customizing specific formatters. So for instance, if I want to use yapf to format Python code instead of the default black, I can set it locally whenever I visit a Python buffer. My updated configuration is as follows:
1
2
3
4
5
6
7
8
9
10
11
12
13
(use-package format-all
:preface
(defun ian/format-code ()
"Auto-format region if active, otherwise format whole buffer."
(interactive)
(if (derived-mode-p 'prolog-mode)
(prolog-indent-buffer)
(format-all-region-or-buffer)))
:config
(global-set-key (kbd "M-F") #'ian/format-code)
(add-hook 'prog-mode-hook #'format-all-ensure-formatter)
(add-hook 'python-mode-hook #'(lambda ()
(setq-local format-all-formatters '(("Python" yapf))))))