An Exploration of Decentralized Moderation on Mastodon

Decentralized Online Social Networks (DOSNs) are rising as a valid alternative to traditional centralized platforms like X (Twitter) and Facebook. Mastodon is to date the most widely recognized decentralized social media service. Thousands of servers have been deployed in the last few years due to the availability of open-source software which allows anyone to easily join the network of interconnected servers. Nonetheless, akin to other social media, Mastodon encompasses instances that host harmful or inappropriate content, which demands moderation. However, the decentralized nature of Mastodon servers poses novel challenges for content moderation. In this work, we explore the dynamics of decentralized moderation on Mastodon through the main tool offered to servers' administrators, namely blocklisting servers to prevent users of an instance from interacting with the content of these servers. Our goal is to shed light on the main traits that characterize blocklisted instances on Mastodon and investigate the emergence of common blocklisting patterns toward specific groups of instances.