One morning, I noticed my Grammarly extension had silently stopped working. It turns out, our security team had blocked it because it was reading a bit more than it should.

Honestly? It makes perfect sense. From a privacy and security standpoint, sending every single line of code, internal document, and private Slack message to a third-party tool is a nightmare.

But I still needed something to catch my typos. I realized I needed a new tool to correct my spelling and style, but it had to run entirely locally on my machine.

Enter LanguageTool. It’s a free, open-source tool that does exactly that. You can self-host the server locally and integrate it into everything from your web browser to VS Code.

Here is my straightforward guide to getting the local server up and running on macOS.

1. Set up the local server

First, we need to install the server, which is a Java application. In my experience, the cleanest way to do this on a Mac is to let Homebrew handle the heavy lifting. Run these commands in your terminal:

brew install languagetool
brew services start languagetool

This installs the LanguageTool server and ensures it boots up automatically whenever you start your Mac.

To verify that the service is actually running, fire this test command into your terminal:

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

2. Configure the browser extension

Install the LanguageTool browser extension ↗ from the Chrome Web Store.

Once installed, open the extension’s settings, navigate to “Advanced settings,” and under the LanguageTool server section, select the Local server option. Boom. Your browser is now checking your grammar locally.

3. LanguageTool in Slack, Mail, and VS Code

LanguageTool also has a macOS-native frontend that provides system-wide support for desktop apps like Slack, Apple Mail, and Microsoft Word. To install it:

brew install --cask languagetool
  • Launch the app from your Applications folder.
  • Open the settings via the menubar icon (LT icon > Gear icon > Settings).
  • Under the “Advanced” tab, set the “API Server URL” to Local server (if you skip this, it will default back to the public cloud server).
  • Under “Active apps,” enable it for Slack or whichever apps you use daily.

What about VS Code? Just install the LanguageTool extension from the marketplace. It automatically detects your local setup and just works.

4. Supercharging it with N-grams (Advanced)

As a bonus, you can download n-grams to drastically improve LanguageTool’s ability to detect context-specific errors, like commonly confused words. It is a massive download, but if you have the disk space, it is absolutely worth it.

  • Download the n-gram dataset ↗ for your preferred language and unzip it. I recommend keeping it tidy in a local directory like ~/ngrams/en.
  • Open your configuration file at /opt/homebrew/etc/languagetool/server.properties.
  • Add the following line, replacing YOUR_USERNAME with your actual Mac username: languageModel=/Users/YOUR_USERNAME/ngrams
  • Restart the service to apply the changes: brew services restart languagetool

5. For the privacy paranoid

If you want absolute certainty that none of your keystrokes are leaking to the internet, you can edit your /etc/hosts file or use a network firewall (like Little Snitch) to explicitly block the public server (api.languagetool.org).

6. Enjoy 🖋️

And that’s it! You now have a powerful, privacy-respecting grammar checker running locally. You get to keep your spelling sharp without failing any corporate security audits.