LanguageTool Setup

Language Check ships with Harper for fast, offline grammar checking. For deeper analysis — advanced grammar rules, style suggestions, and multilingual support — you can optionally connect a LanguageTool server.

This guide walks through every way to get a LanguageTool server running locally.

Quick Start (Docker)

The fastest path. Requires Docker installed.

# From the lang-check repo root (uses the bundled docker-compose.yml)
docker compose up -d

LanguageTool is now running at http://localhost:8010. Skip to Connect to Language Check.

Install LanguageTool

Pick the method that matches your system.

Option A: Docker

Best for most users — no Java required, isolated, easy to update.

Linux

docker pull erikvl87/languagetool
docker run -d --name languagetool -p 8010:8010 --restart unless-stopped erikvl87/languagetool

macOS

docker pull erikvl87/languagetool
docker run -d --name languagetool -p 8010:8010 --restart unless-stopped erikvl87/languagetool

Windows

docker pull erikvl87/languagetool
docker run -d --name languagetool -p 8010:8010 --restart unless-stopped erikvl87/languagetool

Verify it’s running:

curl http://localhost:8010/v2/languages

Option B: Package Manager

Install the standalone Java server via your system package manager.

Linux (apt)

sudo apt update
sudo apt install languagetool
languagetool-server --port 8010 &

Linux (Arch)

sudo pacman -S languagetool
languagetool-server --port 8010 &

macOS (Homebrew)

brew install languagetool
languagetool-server --port 8010 &

Windows (Scoop)

scoop install languagetool
languagetool-server --port 8010

Option C: Manual (JAR)

Works anywhere with Java 11+.

Linux / macOS

1. Install Java if needed:

   java -version  # Check if Java 11+ is installed
   

   If not:

   # Debian/Ubuntu
   sudo apt install default-jre
   
   # macOS
   brew install openjdk
   

2. Download and run LanguageTool:

   curl -L https://languagetool.org/download/LanguageTool-stable.zip -o languagetool.zip
   unzip languagetool.zip
   cd LanguageTool-*/
   
   java -cp languagetool-server.jar \
     org.languagetool.server.HTTPServer \
     --port 8010 \
     --allow-origin "*"
   

Windows

1. Install Java if needed — download from Adoptium (Temurin JRE 11+).

2. Download and run LanguageTool:

   Invoke-WebRequest -Uri "https://languagetool.org/download/LanguageTool-stable.zip" -OutFile languagetool.zip
   Expand-Archive languagetool.zip -DestinationPath .
   cd LanguageTool-*
   
   java -cp languagetool-server.jar `
     org.languagetool.server.HTTPServer `
     --port 8010 `
     --allow-origin "*"
   

Run as a System Service

To have LanguageTool start automatically on boot:

Linux (systemd)

Create /etc/systemd/system/languagetool.service:

[Unit]
Description=LanguageTool Server
After=network.target

[Service]
Type=simple
ExecStart=/usr/bin/java -cp /opt/languagetool/languagetool-server.jar \
  org.languagetool.server.HTTPServer --port 8010 --allow-origin "*"
Restart=on-failure
User=languagetool

[Install]
WantedBy=multi-user.target

Then enable it:

sudo systemctl daemon-reload
sudo systemctl enable --now languagetool

macOS (launchd)

Create ~/Library/LaunchAgents/org.languagetool.server.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
  "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>org.languagetool.server</string>
  <key>ProgramArguments</key>
  <array>
    <string>java</string>
    <string>-cp</string>
    <string>/opt/languagetool/languagetool-server.jar</string>
    <string>org.languagetool.server.HTTPServer</string>
    <string>--port</string>
    <string>8010</string>
    <string>--allow-origin</string>
    <string>*</string>
  </array>
  <key>RunAtLoad</key>
  <true/>
  <key>KeepAlive</key>
  <true/>
</dict>
</plist>

Then load it:

launchctl load ~/Library/LaunchAgents/org.languagetool.server.plist

Docker (auto-restart)

The Docker method already handles this with --restart unless-stopped. To start it after a reboot, just make sure Docker itself starts on boot:

sudo systemctl enable docker

Connect to Language Check

Once LanguageTool is running, enable it in your .languagecheck.yaml:

engines:
  harper: true
  languagetool:
    enabled: true
    url: "http://localhost:8010"

Or change the URL in VS Code settings:

1. Open Settings (Ctrl+,)

2. Search for Language Check

3. Set Engines > LanguageTool to true

4. Set Engines > LanguageTool URL to http://localhost:8010

Multi-Engine Mode

When both Harper and LanguageTool are enabled, they run concurrently and their diagnostics overlay. Duplicate findings at the same text range are automatically deduplicated.

engines:
  harper: true
  languagetool: true

For non-English languages (e.g. spell_language: de-DE), Harper is automatically skipped since it only supports English, and LanguageTool handles all checking.

Verify the Connection

Run a quick check to confirm everything is wired up:

curl -s -X POST "http://localhost:8010/v2/check" \
  -d "language=en-US" \
  -d "text=This is a test sentnce." | python3 -m json.tool

You should see a JSON response with a match for the misspelling “sentnce”.

In VS Code, open any Markdown file — diagnostics from both Harper and LanguageTool will now appear.

Troubleshooting

Connection refused

Make sure the server is actually running on the expected port:

curl http://localhost:8010/v2/languages

If this fails, the server isn’t running. Restart it using the method you chose above.

Slow first check

LanguageTool loads language models on the first request. The first check can take 5-10 seconds; subsequent checks are fast.

Port conflict

If port 8010 is taken, pick another port and update both the server command and your .languagecheck.yaml:

# Start on port 8011 instead
docker run -d --name languagetool -p 8011:8010 erikvl87/languagetool

engines:
  languagetool:
    url: "http://localhost:8011"

Java version errors

LanguageTool requires Java 11+. Check your version with java -version.