CoGrOO – Corretor Gramatical para o (Grammar Checker for is a system that detects grammar  errors in texts written in Portuguese. Natural Language Processing techniques are used to analyze texts in its different layers: sentence, word (morphological analysis), noun phrases, verbal phrases and subject-verb (syntactic analysis). Patterns are applied to the output of the analyses to determine potential grammar errors. Its natural language processing modules could be reused as part of other products that deal with natural language.