HTTP Server

LanguageTool comes with its own embedded HTTP/HTTPS server so you can send a text to LanguageTool via HTTP and get the detected errors back as JSON. This embedded server can be started like this.

WARNING: This approach is only supposed to be used by advanced users who are familiar with using the command line. If you're not, we recommend using the default settings, which use our Cloud servers.

Getting the server

Download the LanguageTool Desktop version for offline use (>170MB) and unzip it.

Starting from Command Line

On the command line, go to the unzipped directory and start LanguageTool using this command:

java -cp languagetool-server.jar org.languagetool.server.HTTPServer --port 8081 --allow-origin "*"

If this fails with an error saying that java cannot be found, install Java 8 or later first.

You can remove --allow-origin "*" if you do not want to use the server from the browser add-on. The server URL to be used in our add-ons is http://localhost:8081/v2 (visit the add-on's options by clicking the cog icon, then open "Experimental settings").

NOTE: This will give you a basic server missing some statistics rules. See here for how to set up those.

Testing the server

You can test the server by calling this URL in your browser:


If you're not just testing, you should use HTTP POST to transfer your data. You can test it like this, using curl:

curl --data "language=en-US&text=a simple test" http://localhost:8081/v2/check

You can specify a file with advanced configuration options for the LT server with --config. Use --help to get information about the supported settings in that file.

For security reasons, the server will not be accessible from other hosts. If you want to run a server for remote users you will need to use the --public option.

Starting from stand-alone LT

Start the stand-alone application and configure it (File -> Options…) to listen on a port that is not used yet (the default port, 8081, should often be okay). This way LanguageTool will also be available in server mode until you stop it.

HTTP Parameters and Result

See the JSON API. Migrate if your code still uses the old XML-based API.

Note that for a server started from a GUI, a user may configure it in the configuration dialog box to disable some unwanted rules. This may be beneficial if the calling program does not allow configuration of the call to the LanguageTool server, and the user wants to enable or disable some checks. However, if the program does disable or enable any rules, then the configuration set by the user will be silently ignored.

Using SSL

Starting with version 2.0, LanguageTool offers an embedded HTTPS server. It works just like the HTTP server described above, but it only supports https. For most production settings, you might prefer to use the HTTP server of LanguageTool and run it behind a Apache or nginx reverse proxy with SSL support. The embedded HTTPS server can be started like this:

java -jar languagetool-server.jar --config is a Java properties file like this:

# Path to Java key store:
keystore = keystore.jks
# Password for the Java key store:
password = my-password
# Maximum text length. Optional - longer texts will not be checked:
maxTextLength = 50000

To run the server you need your own SSL certificate, just like when you protect your webserver using SSL. Assuming you have the required files in PEM/X.509 format, which look like this (the key file):

(lots of random characters here)

…and this (the certificate - there may be more than one):

(lots of random characters here)

You can convert this format to the Java keystore format which LanguageTool needs with openssl and with the keytool command that comes with Java:

cat key server.crt ca.crt >server.pem
openssl pkcs12 -export -out server.p12 -in server.pem
keytool -importkeystore -srckeystore server.p12
    -srcstoretype pkcs12 -destkeystore keystore.jks -deststoretype jks

Note that the key has a password and the keystore has one - currently LanguageTool requires both passwords to be the same.

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