Fedify

MIT · TypeScript · fedify.dev · Repo

Why it exists

ActivityPub in the field means four signature mechanisms — two for HTTP requests, two for documents — JSON that changes shape between servers, deliveries that arrive out of order, and per-server quirks the spec never mentions. Fedify turns that pain into defaults — its author wrote the field guide: Why ActivityPub is hard.

Who it's for

• A new federated app in TypeScript or JavaScript — fedify at full strength. Ghost, Hollo, and Hackers' Pub run it in production.
• An existing app that should federate — integrations for Express, Hono, Next.js, SvelteKit, and a dozen more.
• Anyone tired of hand-writing JSON-LD — the typed vocabulary alone is worth adopting.
• Implementers in other languages — deterministic output makes it a byte-exact answer sheet.

The good part

• The whole federation core is one options object — about two dozen lines in Hollo.
• The inbox is a routing table — signatures are verified before your handler runs.
• An actor is a database lookup — WebFinger, NodeInfo, and key publishing come free.
• Delivery to every follower is one call — fan-out, retries, and ordering included.

The road

Federation grows in stages, each one verifiable before the next: be findable → be followable → speak → listen → interact → grow up. The first three are thin; the fourth is where your real work lives.

Keep in mind

• Persistence is yours — fedify stores nothing; mirroring remote actors and posts is the real work.
• Policy is yours — accepting follows, moderation, honoring deletes.
• Sharp edges exist — immutable vocab, Object shadowing, cross-origin re-fetches, two key types.

Running it

• Split web and worker processes.
• Leave the safety rails on.
• Debug with the CLI, lint in your editor.

See also

• Why ActivityPub is hard

  the author's field guide to what fedify saves you from

  hackers.pub

• Read the code

  production fedify codebases worth an evening's reading

  Hollo Hackers' Pub

• We used fedify, then graduated from it

  our field report from running fedify in production, and moving off it

  blog.atfedi.de