Make Flycheck syntax-check LilyPond files.

With use-package in your init file:

(use-package flycheck
  :ensure t
  :defer t
  :hook (LilyPond-mode . flycheck-mode))

(use-package flycheck-lilypond
  :ensure t)

Or manually from MELPA with M-x package-refresh-contents and M-x package-install RET flycheck-lilypond, then you could have it loaded this way in your init file:

(add-hook 'LilyPond-mode-hook 'flycheck-mode)
(eval-after-load 'flycheck '(require 'flycheck-lilypond)

Just use Flycheck as usual in LilyPond mode.

This program 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.

This program 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.