The Fediverse consists of individual servers, possibly running different software, that talk to each other. One of the challenges in developing for the Fediverse is staying interoperable with all the different deployed software. As the message format standard, ActivityStreams, is extensible through JSON-LD, judging how a message is parsed can be a hard task.

By using ideas from automated testing, we provide an application that determines a baseline for how messages are processed and rendered. The process is simply: run end-to-end tests and record their results. From the test results, a webpage is generated that provides developers with information on how a message is rendered in different applications. We aim to make the framework extensible so new applications can be included.

Federation only protects users if different servers and clients actually understand each other. When implementations diverge, messages break, features silently fail, and users blame decentralization rather than incompatibility, then retreat to centralized platforms that "just work."

The Fediverse Test Framework reduces this interoperability risk by recording how ActivityPub messages are processed and rendered across applications. Developers can see mismatches before users encounter them, helping the Fediverse remain a genuine open network rather than a collection of incompatible silos wearing a federation badge.