Supported federation protocols and standards
- FEP-67ff: FEDERATION.md
- FEP-f1d5: NodeInfo in Fediverse Software
- FEP-8fcf: Followers collection synchronization across servers
- FEP-5feb: Search indexing consent for actors
ActivityPub in Mastodon
Mastodon largely follows the ActivityPub server-to-server specification but it makes uses of some non-standard extensions, some of which are required for interacting with Mastodon at all.
In Mastodon, users are identified by a
domain pair (e.g.,
This is used both for discovery and for unambiguously mentioning users across the fediverse. Furthermore, this is part of Mastodon's database design from its very beginnings.
As a result, Mastodon requires that each ActivityPub actor uniquely maps back to an
acct: URI that can be resolved via WebFinger.
In order to authenticate activities, Mastodon relies on HTTP Signatures, signing every
GET request to other ActivityPub implementations on behalf of the user authoring an activity (for
POST requests) or an actor representing the Mastodon server itself (for most
Mastodon requires all
POST requests to be signed, and MAY require
GET requests to be signed, depending on the configuration of the Mastodon server.