In this work, we present Decidim.viz, a tool to display metrics and statistical information about Decidim instances. Decidim is a digital platform for political participation. We have created a Proof of Concept that analyses a participatory process launched by the European Commission in 2022. Decidim.viz was co-designed with the community of users and researchers of Decidim to guarantee the usefulness of the tool. Decidim.viz is designed as a client-server application that has a web application as a user interface. In addition, the tool provides a RESTful API to make its data reproducible and available to the community.