Despite the ubiquity of XML, research in metrics for XML documents is scarce. This paper proposes and discusses eleven metrics to measure the quality and complexity of XML Schema and conforming XML documents. To provide an easy view of these metrics, two composite indices have been defined to measure quality and complexity. An open source metric analyzer tool for XML Schema has been developed. The tool can easily be extended to add new metrics and alter the composition of the indices to best fit the requirements of a given application.