Developer Resources

A collection of libraries, tools, and resources for building ActivityPub and Fediverse applications.

Libraries

Library listings, with maintenance status taken from package registries and forges, live on the ecosystem pages:

• Libraries overview — what to pick, by language
• Fedify (TypeScript), JavaScript, Python, Go, Rust, Ruby, PHP, other languages

Tools

Testing & Debugging

Tool	Description
FediDB	Fediverse network statistics

Development Utilities

Tool	Description
JSON-LD Playground	Test JSON-LD processing
WebFinger Tester	Test WebFinger discovery

Reference Implementations

Full Servers

Widely deployed servers whose source is worth reading (see Server Software for the full list):

• Microblogging: Mastodon (Ruby), Pleroma (Elixir), Misskey (TypeScript), GoToSocial (Go)
• Link aggregation: Lemmy (Rust)
• Photos: Pixelfed (PHP)
• Video: PeerTube (TypeScript)
• Blogging: WriteFreely (Go); Plume (Rust, little activity since April 2025)

Minimal Examples

Project	Language	Purpose
express-activitypub	Node.js	Small single-user server by Darius Kazemi — readable, but not a security reference
microblog.pub	Python	Single-user server (no GitHub activity since 2023)

Specifications

Core Standards

Specification	URL
ActivityPub	w3.org/TR/activitypub
ActivityStreams 2.0 Core	w3.org/TR/activitystreams-core
ActivityStreams 2.0 Vocabulary	w3.org/TR/activitystreams-vocabulary
JSON-LD	w3.org/TR/json-ld
WebFinger	RFC 7033

De Facto Standards

Specification	Documentation
HTTP Signatures	draft-cavage-12, RFC 9421, SWICG report, Mastodon's profile
NodeInfo	nodeinfo.diaspora.software
Mastodon Extensions	docs.joinmastodon.org

Learning Resources

Tutorials

Resource	Description
ActivityPub Rocks	Official resource site
How to Implement ActivityPub	Mastodon blog tutorial

Diagrams & Visual References

Resource	Description
boyter/activitypub	Sequence diagrams for common flows: Follow, Create, Delete, Announce, Move, WebFinger — a "clean room" implementation reference (MIT)

Books

Resource	Description
ActivityPub: Programming for the Social Web	Evan Prodromou (O'Reilly, 2024) — building ActivityPub clients and servers, by a co-author of the spec
Move Slowly and Build Bridges	Robert W. Gehl (Oxford University Press, 2025) — history and culture of Mastodon and the Fediverse

Community Resources

Forums & Discussion

Resource	Description
SocialHub	Developer community forum
Lemmy Communities	Fediverse discussions
#fediverse:matrix.org	Matrix chat room

News & Updates

Resource	Description
We Distribute	Fediverse news
Fediverse Report	Weekly updates

Curated Lists

Resource	URL
Delightful AP Development	codeberg.org/fediverse/delightful-activitypub-development
Awesome ActivityPub	github.com/BasixKOR/awesome-activitypub
Fediverse.Party Tools	fediverse.party/en/tools

API Documentation

Platform APIs

Platform	Documentation
Mastodon	docs.joinmastodon.org/api
Lemmy	join-lemmy.org/docs
Pixelfed	docs.pixelfed.org
PeerTube	docs.joinpeertube.org/api-rest-reference

Library Documentation

Library	Documentation
Fedify	fedify.dev
go-fed/activity (unmaintained since 2022)	pkg.go.dev/github.com/go-fed/activity
activitypub-federation-rust	docs.rs/activitypub_federation

Quick Reference

Essential URLs

• Specifications: w3.org/TR/activitypub, w3.org/TR/activitystreams-core, w3.org/TR/activitystreams-vocabulary
• Community: socialhub.activitypub.rocks, activitypub.rocks, codeberg.org/fediverse/fep
• Tools: json-ld.org/playground, webfinger.net/lookup, fedidb.org

Common Namespaces

Mastodon's context, including the schema: terms it uses for profile fields (context_helper.rb):

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://w3id.org/security/v1",
    {
      "toot": "http://joinmastodon.org/ns#",
      "schema": "http://schema.org#",
      "PropertyValue": "schema:PropertyValue",
      "value": "schema:value"
    }
  ]
}

Getting Help

Where to Ask Questions

1. SocialHub Forum - Best for implementation questions
2. Matrix Rooms - Real-time help
3. GitHub Issues - Library-specific questions
4. Stack Overflow - the activitypub tag exists but sees little traffic; SocialHub is usually faster

Debugging Tips

// Log incoming activities while debugging (never log secrets in production)
app.post('/inbox', express.raw({ type: '*/*', limit: '1mb' }), (req, res) => {
  console.log('Received activity:', req.body.toString());
  // Verify, then process...
  res.sendStatus(202);
});

To check signatures, don't hand-roll a verifier: see Verifying incoming requests for tested code, or use your framework's built-in verification.

Next Steps

• Getting Started - Begin development
• ActivityPub Protocol - Learn the protocol
• Implementation Guides - Step-by-step guides