Using meta-modeling techniques for defining the abstract syntax of MAS modeling languages(MLs) is a common practice today. This paper presents a framework for evaluating the abstract syntax of MLs. This framework is made of a set of metrics for measuring the metamodels. These metrics help in quantifying three features of the language: specificity, availability, and expressiveness. The specificity and availability metrics are focused on the measurement of the abstract syntax of the final ML products. On the other hand, the specificity metric is focused on the measurement of the abstract syntax of the MLs in its creation and evolution phases. The application of the specificity and availability metrics is exemplified with a study on five agent-oriented MLs. The application of the expressiveness metric is exemplified with the measurement of certain evolution phases of a particular agent-oriented ML. In conclusion, among other things, the presented evaluation framework can be used to compare agent-oriented meta-models and to evaluate the progress of an agent-oriented meta-model with time.