I had different results with the following text, when I copied it onto the website, or when I ran the following command.
The text: “Ich interessiere mich das Auto”
The command: java -jar languagetool-commandline.jar -l de-DE text.txt
The site recognised that the correct sentence is “Ich interessiere mich für das Auto” (The “für” was missing), but the commandline did not deliver any problems.