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LanguageTool (An Open Source alternative to Grammarly) in Docker on a Synology NAS

New guide released12/12/2021
Added note relating to the Desktop App14/02/2022
Updated screenshots and steps for DSM7.116/06/2022
Added new port settings and Docker Bridge Network23/07/2022

What is LanguageTool?

I was looking for a free and also more privacy focused version of Grammarly to help with improving these guides and my writing in general and discovered LanguageTool. It has a free tier as well as premium options. But the part that sold it for me is that it could be self-hosted meaning your data stays local, and its source is open.

Please note that the self-hosted server using Docker can only be used with the Browser and Office add-ons – unfortunately the desktop app does not support self-hosting.

Let’s Begin

In this guide I will take you through the steps of getting it setup in Docker on your Synology NAS.

First up you need to set up a Docker Bridge Network, follow the below guide and then come back here.


When the tool is doing its checks it is a read heavy operation, I found that if you are checking large amounts of text it can take longer when running off of a hard drive array. I would recommend either having an SSD read cache or if you have upgraded your systems’ memory this will speed up things considerably.

Folder Structure

Open up Filestation and create a folder within the docker share called ‘languagetool’

N-Gram Data

In order to make LanguageTool more functional you will want to download the n-grams’ data, this helps the tool detect spelling errors in context. What n-grams do is explained here.

Go to the site below and download the data for your language, you can save the zip file to your computer, the English zip is around 8Gb.

Once the zip file has downloaded we need to upload it to our Docker share and unzip it.

Go back into Filestation and into the ‘languagetool’ folder we created, click on ‘Upload’ and upload the zip file.

Select Upload

You can see the progress in the top right side of DSM.

Once the upload has been completed we need to unzip/extract the n-grams’ data, you do this by right-clicking on the zip file, selecting ‘Extract’ then ‘Extract Here’ from the sub menu. This will likely take a few minutes. The final extracted size for the files is around 16Gb.

After extraction, you should have a new subfolder called ‘en’ or the language code of the language you downloaded, you can delete the zip file if you wish.

Downloading the LanguageTool Image

Now we can look at getting the container set up, open up Docker and go into the ‘Registry’ tab.

Search for LanguageTool in the top right of the window, for this guide we will be using the container by erikvl87.

Click on Download and when asked to choose a tag, select ‘latest’

You can check the status of the download over on the ‘Image’ tab, it will take a few minutes depending on the speed of your internet connection.

Setting up the container

In Docker click on the ‘Image’ tab, in the list of your containers select the ‘LanguageTool’ image and click on ‘Launch’

You will be greeted with the Network screen, we will be using the ‘synobridge’ network we created earlier select it from the list and click Next.

General Settings

Next you will be greeted with the General Settings screen, this is where you can start specifying some of your preferences.

You can change the name of the container to anything you like, and you may want to enable Auto Restart as this will ensure LanguageTool starts automatically if you reboot your NAS.

Now click on the Advanced Settings button.


We need to set a few environment variables, these tell the container to configure itself based on these additional options.

Click on the add button and enter the following details as per the table, it is important these are added exactly as shown.


You do not need to set up anything on these tabs.

Press ‘Save’ to go back to the initial setup screen, then press ‘Next’

Port Settings

We won’t be changing any of the ports the container uses. You can repeat the ones shown on the right side of the settings page ‘Container Port’ onto the left side ‘Local Port’ once you have done this press ‘Next’.

Volume Settings

We will now be specifying the directory where we saved our n-grams data from earlier.

Click on ‘Add Folder’ then navigate to the ‘languagetool’ folder we created and click on ‘Select’

In the ‘Mount path’ section enter /ngrams


You have now completed the setup of the container.

You will be shown an overall summary of the settings we have specified, this is a good time to double-check everything is correct. Finally, click on Done and the container should start to boot.

Configuring the Extensions

With the container running we can now configure the specific extensions LanguageTool offers to point its queries to our local version of the tool. I am using the Chrome plugin as an example, but the premise is the same for each one.

Once the extension has installed head into its settings (where these are located will depend on your browser)

First up I have Picky mode and synonyms enabled

Then you will see a section called ‘Experimental settings (only for advanced users)

In this section we are going to select the ‘Other server’ option and then enter ‘http://YOURNASIP:8010/v2’ ensuring you have entered your own IP.

Let’s test to see if everything is working correctly.

Open up and copy the text below into the ‘New Paste’ section.

Dear Jane,

I was delighted to read you're letter last week. Its always a pleasure to recieve the latest news and to here that you and your family had a great summer.

We spent last week at the beach and had so much fun on the sand and in the water exploring the coast we weren't prepared for the rains that came at the end of the vacation. The best parts of the trip was the opportunities to sightsee and relax.

My kids are back in school to. I find their are less things to worry about now that the kids are at school all day. There is plenty of fun things to do in the summer, but by August, I've running out of ideas. I've excepted the fact that we'll have to think up brand-new activities next summer; hoping to round up some creative ideas soon.

Thanks again for your letter!


You will see an animation in the bottom right, this means the tool is checking the sentences, after a few seconds you will see the results of the analysis with the suggested changes highlighted.

You are now all set up.

Docker Compose

Follow the guide above until you reach the ‘Downloading the LanguageTool Image’ section. You can then use the code below saved as languagetool.yml in the ‘/docker/languagetool’ share this will do the rest of the process above in one quick command via SSH.

version: "3.8"
    image: erikvl87/languagetool
    container_name: languagetool
    network_mode: host
      - langtool_languageModel=/ngrams
      - Java_Xms=512m
      - Java_Xmx=1g
      - /volume1/docker/languagetool:/ngrams
      - 8010:8010
    network_mode: synobridge
sudo docker-compose -f /volume1/docker/languagetool/
languagetool.yml up -d

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  1. Neil Neil

    Hi there,

    I followed your guide, and did not touch the port settings. This failed, as it defaulted to “auto” for the local port. This created a local port of 49xxx, meaning that the server location in the extension configuration was wrong. I had to change the local port from “auto” to “8010”. Working fine thereafter.

    • Dr_Frankenstein Dr_Frankenstein

      Hey Neil, you might have skipped the Network section as you can tick the Use Same Network as host option which will avoid it assigning random ports. Nothing wrong with manually setting one though

  2. This would have been great; however, it looks like they have removed the ability to use your own provision within the latest versions of the plugin.

    If you look at their support notes:

    There’s a requirement to download the old version of the desktop app to be able to do what this post is about. I only discovered this once I was all setup and trying to add the “Other server”

    • Dr_Frankenstein Dr_Frankenstein

      The browser plugins should still work, I will have a look to see what version of the desktop app is required for your own hosted version.
      – I will have a read of the support article to see if I can add to the guide how to use the desktop app as I have primarily been using the browser add-ons.

    • Dr_Frankenstein Dr_Frankenstein

      Further to my previous reply – I have had read, and this method is not supported using the old desktop app, you can self-host on a local machine but not remotely with it.

      This is a real shame as it works really well with the browser add-ons and the various office add-ons do support the docker set up as I am using the LibreOffice one.

  3. Junior Junior

    Awesome! Thanks

  4. tempata tempata

    Thank you. It’s very interesting. I’m just not sure about one thing. I’ve downloaded just EN ngrams files, but if I set in the preferred language settings another language (that is not downloaded to my FileStation) it will check it and correct spelling right.

    This is strange, so it connects to their servers to check that other language?

    Thank you for your answer.

    • Dr_Frankenstein Dr_Frankenstein

      Hey, it will check spellings with its built in basic data, the engrams provide it with additional abilities such as offering alternatives etc. So it’s still all local even the other languages are baked in to the base image.

      • tempata tempata

        Oh, wow. That’s nice. Thank you for prompt answer.

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