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Language Tool App


LanguageTool’s multilingual grammar, style, and spell checker is used by millions of people around the world


By default, the app's API is public. To avoid misuse, it's best to change the URL to some secret. To do so:

  • Edit /app/data/env using the File manager

  • Change API_PATH_PREFIX to some secret. You can generate a secret using pwgen -1s 6 .

  • Restart the app.

In the apps, use<secret>/v2 as the URL instead of the default

To test, if hushhush is the secret:

curl -d "text=Hello world" -d "language=de-DE"

Use alphanumerals for the secret

The secret is part of the URL. For this reason, keep it simple and use only alphanumerals for the secret.


LanguageTool can optionally make use of large n-gram data sets to detect errors with words that are often confused, like their and there.

The n-gram data set is huge and thus not part of the LT download. The install path is the first argument for the download command below. The default is /app/data/ngrams but you can use e.g. a volume path if you don't want ngrams to be part of your backup.

To download the n-gram data set of a language:

  • Open a Web Terminal and run the command below. Replace the argument /app/data/ngrams with your desired path (e.g. a volume) if you don't want ngrams to be part of your backup .
# /app/pkg/ /app/data/ngrams en es
==> Installing en ngram dataset from
/tmp/ 100%[================================================================>]   8.35G   112MB/s    in 77s     
==> Unpacking en ngram dataset
Archive:  /tmp/
   creating: en/
   creating: en/3grams/
  inflating: en/3grams/_1e4.fdt      
  inflating: en/3grams/       
 extracting: en/3grams/_1e4.nvd      


  inflating: en/1grams/        
==> en ngram dataset has been installed.
==> Done

Set NGRAM_DATASET_PATH=/app/data/ngrams in /app/data/env and restart the app.
  • Open /app/data/env using the file manager and check that NGRAM_DATASET_PATH is set to the correct path.

  • Restart the app.

Large data set

n-gram data sets are large. For example, the en is around 14GB and de is 3GB.