Note: XDG is broken - see https://mailarchive.ietf.org/arch/msg/art/EEAIbW8mtUGOQKPrfMkLFrjE83s/ The ActivityPub mimetypes are application/ld+json; profile="https://www.w3.org/ns/activitystreams" application/activity+json While mimetypes are usually called with paths (except for x-scheme-handler ones), they can also be called with URIs sometimes. It'd be nice to lean into those.