Flycheck is a modern on-the-fly syntax checking extension for GNU Emacs 24, intended as replacement for the older Flymake extension which is part of GNU Emacs.

It uses various syntax checking and linting tools to check the contents of buffers, and reports warnings and errors directly in the buffer, or in an optional error list. The following screenshow shows Flycheck at work in a Haskell buffer, using GHC and Hlint for syntax checking:

The color theme in this screencast is Solarized Light, with the the Source Code Pro font.

• Supports over 30 programming and markup languages with more than 70 different syntax checking tools
• Fully automatic, fail-safe, on-the-fly syntax checking in background
• Nice error indication and highlighting
• Optional error list popup
• Many customization options
• A comprehensive manual
• A simple interface to define new syntax checkers
• A “doesn't get in your way” guarantee
• Many 3rd party extensions

Flycheck needs GNU Emacs 24 on a Unix system, and additionally external syntax checking programs for the languages you use. See Supported Languages for more information.

Flycheck does not officially support Windows, but tries to maintain Windows compatibility and should generally work fine on Windows, too.

Install Flycheck from MELPA or MELPA Stable with:

M-x package-install RET flycheck

In your Cask file:

(source gnu)
(source melpa)

(depends-on "flycheck")

Then add the following to your init file:

(add-hook 'after-init-hook #'global-flycheck-mode)

If you don’t know where your init file is, look at the value of the variable user-init-file with C-h v user-init-file.

See Installation and Quick start for more information.

Documentation is available at http://www.flycheck.org:

• Quick start (tutorial)
• User manual (reference information)

• Issue tracker
• Github
• Contribution guidelines

• Contributors
• Credits

Flycheck is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

Flycheck is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.

See COPYING for details.

The Flycheck documenation is free documentation: you can copy, distribute and/or modify it under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is available at https://github.com/flycheck/flycheck/blob/master/doc/fdl.txt.

Alternatively, you may copy, distribute and/or modify the Flycheck documentation under the terms of the Creative Commons Attribution-ShareAlike 4.0 International Public License. A copy of the license can be obtained at https://creativecommons.org/licenses/by-sa/4.0/legalcode.

Permission is granted to copy, distribute and/or modify the Flycheck logo in /flycheck.svg under the terms of the Creative Commons Attribution-ShareAlike 4.0 International Public License. A copy of the license can be obtained at https://creativecommons.org/licenses/by-sa/4.0/legalcode.