UK's Online Safety Act: A Practical Guide for Small Mastodon Hosts

The introduction of the UK's Online Safety Act (OSA) has raised questions and concerns for administrators of smaller, community-focused online platforms. A key point of uncertainty is how the law applies to decentralized, federated services like Mastodon, where a small, self-hosted instance can connect to a much larger network.

Understanding the Scope of the OSA

A primary point of clarification is that the OSA is not a one-size-fits-all piece of legislation. It establishes different tiers of regulation based on the size and risk profile of a service. According to guidance from the regulator, Ofcom, services with fewer than 7 million users in the UK are considered "smaller" and are subject to lighter requirements.

For a solo user self-hosting an instance for personal use, the act likely poses no concern. For small community instances, the obligations largely center on duties of care that are already considered best practice for online communities.

Core Requirements and Best Practices

Many of the duties imposed by the OSA on smaller services are actions that responsible administrators should already be taking. These include:

• Having a Code of Conduct: Clearly defining acceptable user behavior.
• Moderation and Complaint Handling: Implementing a system for users to report content and for administrators to review and act on those reports.
• Filtering Illegal Content: Using available tools, such as CDN-level filters or hash-matching databases, to proactively block known Child Sexual Abuse Material (CSAM).

The Debate on Legal Risk

The discussion highlighted a significant debate about the level of real-world risk for volunteer administrators.

One perspective is pragmatic, suggesting that legal systems are not typically vindictive. If an administrator discovers illegal content on their server (especially content federated from elsewhere), the crucial factor is their response. Taking prompt action to remove the content and aid authorities is viewed very differently from knowingly hosting or distributing it. From this viewpoint, good-faith moderation is a strong defense.

However, a more cautious perspective emphasizes the potential for severe consequences. The Fediverse is vast, and an instance can inadvertently cache illegal material from a poorly moderated server it federates with. The argument is that the law is complex, precedent is scarce, and the financial and personal cost of defending oneself in court could be life-ruining, regardless of the final verdict. This view posits that a judge may not fully grasp the technical nuances of federation, placing the administrator in a precarious position.

Practical Steps to Mitigate Risk

Several practical strategies were suggested for administrators looking to reduce their liability under the OSA:

1. Whitelist Federation: Instead of federating openly with any instance, adopt a "whitelist" approach. Only connect and exchange content with a curated list of other instances that are known to be well-moderated. This is arguably the most effective technical control.
2. Know Your Users: The risk is lowest when an instance is run for a small group of known and trusted individuals.
3. Consult Official Resources: Ofcom provides a regulation checker and detailed guidance documents to help services understand their obligations.