Install LanguageTool version 3.0 or later (and java) https://languagetool.org/

Put this file into load-path'ed directory, and byte compile it if desired. And put the following expression into your ~/.emacs.

(require 'langtool)

Or use Melpa (https://melpa.org/)

Confirmed working on following environment

java --version

openjdk 17.0.4 2022-07-19
OpenJDK Runtime Environment (build 17.0.4+8-Debian-1deb11u1)
OpenJDK 64-Bit Server VM (build 17.0.4+8-Debian-1deb11u1, mixed mode, sharing)

Can be downloaded from here

java -jar languagetool-commandline.jar --version

LanguageTool version 6.0 (2022-12-29 12:13:11 +0000, e44dbb0)

langtool.el have 3 types of client.

1. Command line

This setting should be set, if you use rest of clients, to get full of completion support. And you should be set the variables before load this library.

(setq langtool-language-tool-jar "/path/to/languagetool-commandline.jar")
(require 'langtool)

Alternatively, you can set the classpath where LanguageTool's jars reside (e.g. ArchLinux):

(setq langtool-java-classpath
      "/usr/share/languagetool:/usr/share/java/languagetool/*")
(require 'langtool)

You can set a script that hold java setting (e.g. Gentoo):

(setq langtool-bin "/path/to/your/langtool")
(require 'langtool)

2. HTTP server & client

You can use HTTP server implementation. This is very fast after listen server, but has security risk if there are multiple user on a same host.

(setq langtool-language-tool-server-jar "/path/to/languagetool-server.jar")

You can change HTTP server port number like following.

(setq langtool-server-user-arguments '("-p" "8082"))

3. HTTP client

If you have running HTTP LanguageTool server instance on any machine:

(setq langtool-http-server-host "localhost"
      langtool-http-server-port 8082)

Now testing although, that running instance is working under HTTPSServer or via general ssl support (e.g. nginx) following may be working. Again, this is now testing, so please open issue when the ssl/tls connection is not working.

(setq langtool-http-server-stream-type 'tls)

• Key binding if you desired.

(global-set-key "\C-x4w" 'langtool-check)
(global-set-key "\C-x4W" 'langtool-check-done)
(global-set-key "\C-x4l" 'langtool-switch-default-language)
(global-set-key "\C-x44" 'langtool-show-message-at-point)
(global-set-key "\C-x4c" 'langtool-interactive-correction)

• Default language is detected by LanguageTool automatically. Please set langtool-default-language if you need specific language.

(setq langtool-default-language "en-US")

Otherwise, invoke M-x langtool-check with C-u (universal-argument)

• Currently GNU java version is not working. Please change the variable to your favorite java executable.

(setq langtool-java-bin "/path/to/java")

• Maybe your LanguageTool have launcher. (e.g. Gentoo) You need to set langtool-bin. See #24

(setq langtool-bin "/usr/bin/languagetool")

• Maybe you want to specify your mother tongue.

(setq langtool-mother-tongue "en")

• To customize LanguageTool commandline arguments.

(setq langtool-java-user-arguments '("-Dfile.encoding=UTF-8"))

You can also make the variable to buffer local like following:

(add-hook '**SOME**-mode-hook
          (lambda () (set (make-local-variable 'langtool-java-user-arguments)
                         '("-Dfile.encoding=UTF-8"))))

NOTE: Although there is no good example, langtool-user-arguments is a similar custom variable.

• To check current buffer and show warnings.

M-x langtool-check

Check with different language. You can complete supported language with C-i/TAB

C-u M-x langtool-check

• To correct marker follow LanguageTool suggestions.

M-x langtool-correct-buffer

• Go to warning point you can see a report from LanguageTool. Otherwise:

M-x langtool-show-message-at-point

• You can optionally use extension package langtool-popup in this repository. To show automatically popup the cursor.

• To finish checking. All langtool marker is removed.

M-x langtool-check-done