The Unified Modeling Language (UML) is a de facto standard notation for software documentation, effective design metrics increasingly must work with UML diagrams as input. Some tools have the ability to calculate design metrics from UML diagrams, but this activity can benefit from relying on Web services created with an open-source solutions to calculate the metrics. This article describes how to use a Web Service for Calculating the metrics of UML class diagrams. The authors present a Web service that they have created. It uses SOAP messages, typically conveyed using HTTP, with XML serialization. Thus the calculation of UML metrics can be inserted in any development environment and used as a source of early feedback to architects and developers.