LanguageTool Docker Image

LanguageTool is an Open Source proofreading software for English, French, German, Polish, Russian, and more than 20 other languages. It finds many errors that a simple spell checker cannot detect.

The source repository can be found on GitHub. The Docker Hub repository can be found on Docker Hub.

Features

• Built directly from LanguageTool repository tags since official release ZIPs were discontinued after v6.6
• Built on latest Alpine 3.24 base image
• Multi-arch: supports linux/amd64 and linux/arm64
• Custom Eclipse Temurin 21 JRE (optimized with required modules only)
• Uses tini to handle container signals properly
• includes fasttext
• container starts as privileged user (=root) and executes LanguageTool as unprivileged user (default)
  • optional: container fixes folder ownership for ngrams and fasttext folders (default)
  • optional: support user mapping (make sure to check MAP_UID and MAP_GID below)
  • optional: works with read-only filesystem (uses nss_wrapper for user mapping)
• container can be started as unprivileged user instead of root user
  • optional: works with read-only filesystem
• optional: downloads ngram language modules if configured (if they don't already exist)
• optional: downloads fasttext module (if it doesn't already exist)
• optional: allows to set log level

Setup

The following subsections show usage examples. An example compose file can be downloaded from docker-compose.yml.

Start container as root user with read-only filesystem, start LanguageTool as MAP_UID:MAP_GID

Start the container as root user with all required capabilities to fix file ownership, and execute LanguageTool as unprivileged user.

Docker CLI Usage

docker run -d \
  --name languagetool \
  --restart unless-stopped \
  --cap-drop ALL \
  --cap-add CAP_CHOWN \
  --cap-add CAP_DAC_OVERRIDE \
  --cap-add CAP_SETUID \
  --cap-add CAP_SETGID \
  --security-opt no-new-privileges \
  --publish 8081:8081 \
  --env download_ngrams_for_langs=en \
  --env MAP_UID=783 \
  --env MAG_GID=783 \
  --read-only \
  --tmpfs /tmp:exec \
  --volume $PWD/ngrams:/ngrams \
  --volume $PWD/fasttext:/fasttext \
  meyay/languagetool:latest

Docker Compose Usage

---
services:
  languagetool:
    image: meyay/languagetool:latest
    container_name: languagetool
    restart: unless-stopped
    read_only: true
    tmpfs:
      - /tmp:exec
    cap_drop:
      - ALL
    cap_add:
      - CAP_CHOWN
      - CAP_DAC_OVERRIDE
      - CAP_SETUID
      - CAP_SETGID
    security_opt:
      - no-new-privileges
    ports:
      - 8081:8081
    environment:
      download_ngrams_for_langs: en
      MAP_UID: 783
      MAP_GID: 783
    volumes:
      - ./ngrams:/ngrams
      - ./fasttext:/fasttext

Start container as unprivileged user with read-only filesystem

Start the container as unprivileged user specified by the --user argument. The container will neither try to fix file ownership, nor does it require any additional capabilities.

You need to make sure the directories bound as volume do exist, and are owned by the same user and/or group specified in the --userargument!

This is the recommended way to run the container.

Docker CLI

docker run -d \
  --name languagetool \
  --restart unless-stopped \
  --cap-drop ALL \
  --security-opt no-new-privileges \
  --publish 8081:8081 \
  --env download_ngrams_for_langs=en \
  --user 783:783 \
  --read-only \
  --tmpfs /tmp:exec \
  --volume $PWD/ngrams:/ngrams \
  --volume $PWD/fasttext:/fasttext \
  meyay/languagetool:latest

Docker Compose

---
services:
  languagetool:
    image: meyay/languagetool:latest
    container_name: languagetool
    restart: unless-stopped
    user: "783:783"
    read_only: true
    tmpfs:
      - /tmp:exec
    cap_drop:
      - ALL
    security_opt:
      - no-new-privileges
    ports:
      - 8081:8081
    environment:
      download_ngrams_for_langs: en
    volumes:
      - ./ngrams:/ngrams
      - ./fasttext:/fasttext

Usage

You need to install and use one of the add-ons and configure it to use the self-hosted LanguageTool server http://{ip-of-your-docker-host}:{published host port}/v2. The self-hosted LanguageTool server does not come with its own UI or supports user authentication!

NOTE: Some add-ons require https connections, which is not (and will not be) supported by this image. You will need to put a reverse proxy in front of it to take care of the TLS termination.

Capabilities

If the container is started as unprivileged user, the capabilities CAP_CHOWN CAP_DAC_OVERRIDE, CAP_SETUID and CAP_SETGID, are not required, and can be omitted. If the container is started as privileged user (default), and the environment variable DISABLE_FILE_OWNER_FIX is set to true, the capabilities CAP_CHOWN and CAP_DAC_OVERRIDE are not required and can be omitted.

Ports

The self-hosted LanguageTool server in the container is listening on port 8081 by default.

It can be changed using the environment variable LISTEN_PORT.

Volumes

Required	Container Path	DESCRIPTION
no	/ngrams	Location to store the ngram language models. If container is started as unprivileged user, make sure the host path is owned by the user and/or group that starts the container.
no	/fasttext	Location to store the fasttext model. If container is started as unprivileged user, make sure the host path is owned by the user and/or group that starts the container.
yes	/tmp	Location to store the created logback.xml and config.property. Preferably a tmpfs mount with exec permissions.

Restrictions if only required volumes are used:

• privileged container: ngram language models and fasttext model will be written into the container filesystem.
• read-only filesystem: neither ngram language models, nor fasttext model can be used.
• unprivileged container: neither ngram language models, nor fasttext model can be used.

Parameters

The environment parameters are split into two halves, separated by an equal or colon, the left-hand side represents the variable name (use it as is), the right-hand side the value (change if necessary).

ENV	DEFAULT	DESCRIPTION
download_ngrams_for_langs	none	Optional: Comma separated list of languages to download ngrams for. Skips download if the ngrams for that language already exist. Valid languages: en, de, es, fr and nl. Example value: en,de
langtool_languageModel	/ngrams	Optional: The base path to the ngrams models.
langtool_fasttextBinary	/usr/local/bin/fasttext	Optional: Path to the fasttext binary. Change only if you want to test your own compiled binary. Don't forget to map it into the container as volume.
langtool_fasttextModel	/fasttext/lid.176.bin	Optional: The container path to the fasttext model binary. If the variable is set, the fasttext model will be downloaded if doesn't exist yet.
langtool_*		Optional: An arbitrary LanguageTool configuration, consisting of the prefix langtool_ and the key name as written in the config file. Execute docker run -ti --rm meyay/languagetool help to see the list of config options.
JAVA_XMS	256m	Optional: Minimum size of the Java heap space. Valid suffixes are m for megabytes and g for gigabytes.
JAVA_XMX	1536m	Optional: Maximum size of the Java heap space. Valid suffixes are m for megabytes and g for gigabytes. Set a higher value if you experience OOM kills.
JAVA_GC	ShenandoahGC	Optional: Configure the garbage collector the JVM will use. Valid options are: SerialGC, ParallelGC, ParNewGC, G1GC, ZGC, ShenandoahGC
JAVA_OPTS		Optional: Set you own custom Java options for the JVM. This will render the other JAVA_* options useless.
LISTEN_PORT	8081	Optional: Set listen port of the self-hosted LanguageTool server inside the container.
MAP_UID	783	Optional: UID of the user inside the container that runs LanguageTool. If you encounter permission problems with your volumes, make sure to set the parameter to the UID of the host folder owner.
MAP_GID	783	Optional: GID of the user inside the container that runs LanguageTool. If you encounter permission problems with your volumes, make sure to set the parameter to the GID of the host folder owner.
LOG_LEVEL	INFO	Optional: Set log level for LanguageTool. Valid options are: TRACE, DEBUG, INFO, WARN, ERROR.
DISABLE_FILE_OWNER_FIX	false	Optional: Disables file ownership fix, if set to true. Will be used implicitly, if the container is started with an upriviliged user. The Valid options are: true, anything else is treated as false.
DISABLE_FASTTEXT	false	Optional: Disables fasttext, if set to true, neither the model is downloaded, nor fasttext enabled in LanguageTool. The Valid options are: true, anything else is treated as false.
DEBUG_ENTRYPOINT		Optional: Enables debug logs, if set to true. The Valid options are: true, anything else is treated as false.
CONTAINER_MODE	default	Optional: Configure the containers behavior. Docker users use default. Kubernetes users can use download-only with initContainers, and start the main container with default.

Fasttext support

The image comes with the Alpine fasttext package. If it does not work for you, you can build a custom image to compile the fasttext binary using CPU optimizations your CPU actually understands (supports both amd64 and arm64):

git clone  https://github.com/meyayl/docker-languagetool.git
cd docker-languagetool
sudo docker build -t meyay/languagetool:latest -f Dockerfile.fasttext .

As alternative method, sudo make docker_build can be used to build your custom image.

Once the image is build, you can docker compose up -d like you would do with the images hosted on Docker Hub.

NOTE: Synology users can find a git package in the SynoCommunity repository.

Changelog

See CHANGELOG.md for the full release history.