Developer Documentation for ActivityPub & Fediverse

Documentation

Getting Started

New to ActivityPub? Start here with our beginner-friendly guides covering core concepts, your first server, and understanding federation.

📋

Protocol Specifications

Deep-dive into ActivityPub, ActivityStreams 2.0, WebFinger, HTTP Signatures, and other protocols powering the Fediverse.

🔧

Implementation Guides

Step-by-step tutorials for building actors, handling activities, implementing follows, posts, likes, and more.

📖

API Reference

Complete reference for object types, activity types, properties, endpoints, and security implementations.

🌐

Ecosystem Directory

Explore server software, libraries, SDKs, client apps, bridges, and tools across the Fediverse ecosystem.

🛠️

Testing & Debugging

Checklists, debugging tips, and pointers to testing tools that help you build and debug your ActivityPub implementation.

Quick Links

📄ActivityPub Spec (W3C)📄ActivityStreams Core 💬SocialHub Forum 📝FEP Repository 👥Fediverse Developers ✅Troubleshooting

Platforms Covered

Build software that federates with ~14M registered accounts (~1.3M monthly active) on 41,098 servers. Account counts from FediDB, latest stable versions from each project's releases, as of 15 October 2026.

Mastodon8.5M accounts · 4.7.3

Lemmy369K accounts · 0.19.20

Pixelfed1.2M accounts · 0.14.4

PeerTube560K accounts · 8.3.1

Misskey1.3M accounts · 2026.10.0

Pleroma54K accounts

GoToSocial755 accounts · 0.22.2

Friendica18K accounts · 2026.05-1

ActivityPub is a W3C Recommendation — the open standard powering the decentralized social web.