Abstract. Model quality is still an open issue, and a first step towards quality could be a style guide. A style guide is a set of rules aiming to help the developer improving models in many directions such as good practices, methodology, consistency, modeling or architectural style, conventions conformance etc. First, this paper attempts to clarify the meaning of notions being used such as rule or modeling domain semantics. Then, several examples illustrate a possible classification of rules, and the verification process is detailed. A style guide is not universal: each project manager should be able to customize his/her set of rules according to specific needs. In addition to rules expressed in OCL, we describe a user interface to facilitate the specification of rules based on quantifiers, along with the translation of these rules into OCL.