Ever wanted to fix a rule in LanguageTool so it doesn't give a false alarm? Every wanted to add a new rule to catch your favorite mistake? If you didn't because you think it's difficult - it's not (although having used XML helps). Check out our new "three-minute introduction" at http://www.languagetool.org/development/#intro which will show you how to add a new simple rule easily.
We have now also added a rule creation page at http://www.languagetool.org/ruleeditor/ which will help you with writing simple rules. This way you don't have to learn the XML syntax, at least for simple rules. It also tests the rule against Wikipedia documents to catch false alarms. Feedback is very welcome.