While there are spell-checkers but AFAIK they are limited to spell-checking. Are there any grammar-checking utilities in free software and more precisely Debian. Even if not in Debian, then in free software. I am using the spell-checking tag as those folks would probably be also interested in this.
You can try this Python library:
You should not look for a Linux program that does this, but for a Python / Java / PHP / C++ app that does this. Any language that can run under Linux will do. I've googled for "python grammar checker".
LibreOffice Writer by default checks grammar as you type. To turn this feature on or off, go to
Spelling and Grammar, click the
Options... button, and check or uncheck
Check grammar as you type. Note:
Spelling and Grammar will only open if your document is not empty (i.e., contains some text). Tested in Debian 9/Stretch.
If you don't have
LibreOffice installed, get it with
sudo apt-get install libreoffice.
Abiword also has grammar checking. In Debian, install with
sudo apt-get install abiword abiword-plugin-grammar. These packages are present in all current Debian GNU/Linux flavors (Stable 8/Jessie, Testing 9/Stretch, and Unstable/Sid).
Abiword, go to
Spell Checking tab, and place a checkmark by the option
Check grammar as you type to activate the grammar checking.
For both of these, possible grammar errors will be marked by a wavy blue or green underline.
There exists this, which is a Java library/application which comes with word processor plugins and a Web API.
You can also use Gramma - it is an interactive command-line grammar checker, it is written in Node.js, but you can also download a standalone binary for Linux: https://github.com/caderek/gramma