This paper describes an ongoing Portuguese Language grammar checker project, called CoGrOO1-Corretor Gramatical para OpenOffice (Grammar Checker for OpenOffice), based on CETENFOLHA, a Brazilian Portuguese morphosyntactic annotated Corpus. Two of its features are highlighted: - hybrid architecture, mixing rules and statistics; - free software project. This project aims at checking grammatical errors such as nominal and verbal agreement, “crase” (the coalescence of preposition “a” (to) + definitive singular determiner “a” yielding “à”), nominal and verbal government and other common errors in Brazilian Portuguese Language. We also present some empirical results based on the implemented techniques.