kb-fediverse-federation-md

FEDERATION.md (FEP-67ff) — Complete Reference

Overview

FEDERATION.md is a convention for documenting how a project implements federation protocols. Formalized as FEP-67ff (authored by silverpill, status FINAL, finalized 2024-09-22), it provides a standardized location and format for interoperability documentation — analogous to README.md for project description or CONTRIBUTING.md for contributor guidelines.

The convention originated in January 2020 when Darius Kazemi (creator of gath.io) proposed a standard documentation file after struggling to understand how other servers handled federation. It grew organically to 12+ implementations before silverpill formalized it as a FEP in April 2023. Over 40 projects have now adopted it, including Mastodon, Pixelfed, Lemmy, WordPress ActivityPub, GoToSocial, and PeerTube.

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1. Specification Requirements (RFC 2119)

Only two hard requirements:

1. It MUST be a valid Markdown document
2. It MUST be located in the root of a project's code repository (or, if documentation is located elsewhere, contain a link to that location)

Soft requirements (SHOULD):

• It SHOULD enumerate implemented federation protocols and standards
• It SHOULD list supported Fediverse Enhancement Proposals (FEPs)

The file "can have arbitrary structure and content" — the spec deliberately avoids mandating a rigid format, allowing each project to document what matters most for its federation behavior.

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2. Suggested Template

The specification provides a reference template with these sections:

Supported Federation Protocols and Standards

List the protocols the project implements:

## Supported federation protocols and standards

- [ActivityPub](https://www.w3.org/TR/activitypub/) (Server-to-Server)
- [WebFinger](https://webfinger.net/)
- [HTTP Signatures](https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures)
- [NodeInfo](https://nodeinfo.diaspora.software/)

Supported FEPs

List adopted Fediverse Enhancement Proposals:

## Supported FEPs

- [FEP-67ff: FEDERATION.md](https://codeberg.org/fediverse/fep/src/branch/main/fep/67ff/fep-67ff.md)
- [FEP-f1d5: NodeInfo in Fediverse Software](https://codeberg.org/fediverse/fep/src/branch/main/fep/f1d5/fep-f1d5.md)

ActivityPub-Specific Documentation

Detailed sections covering:

• Profiles / actors
• Posts / objects
• Addressing and delivery
• Content limits
• Non-standard extensions
• Known interoperability quirks

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3. The Problem FEDERATION.md Solves

ActivityPub is a protocol specification that leaves many implementation details up to individual servers. Different implementations make different choices about:

• Which Activity types they handle (some ignore Like, some ignore Announce)
• How they represent custom content (BookWyrm reviews, Lemmy votes, Pixelfed photos)
• What non-standard extensions they require (Mastodon's HTTP Signature requirements)
• How they handle edge cases (username changes, content limits, private posts)

Before FEDERATION.md, the only way to understand another implementation's behavior was to read their source code, reverse-engineer through testing, or ask on forums. This was particularly painful because the Fediverse has dozens of implementations in different programming languages.

FEDERATION.md provides a single, predictable file location where developers can find all federation-relevant documentation. By placing it at the repository root as a Markdown file, it follows established open-source conventions (like README.md, CONTRIBUTING.md, LICENSE) and is immediately accessible via any code hosting platform.

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4. Real-World Examples

Mastodon's FEDERATION.md

Mastodon's file documents:

• Protocols: ActivityPub (S2S), WebFinger, HTTP Signatures, NodeInfo
• FEPs: FEP-67ff, FEP-f1d5, FEP-8fcf, FEP-5feb, FEP-044f, and others
• Detailed sections: profiles/actors, posts, addressing, content limits, non-standard extensions
• Notes that Mastodon "largely follows the ActivityPub server-to-server specification but makes use of some non-standard extensions, some of which are required for interacting with Mastodon at all"

WordPress ActivityPub Plugin's FEDERATION.md

Documents support for:

• ActivityPub S2S, WebFinger, HTTP Signatures, NodeInfo
• Various FEPs including FEP-67ff itself and FEP-3b86 (Activity Intents)
• Notes that it "largely follows ActivityPub's server-to-server specification, but makes use of some non-standard extensions"

Both files follow a similar structure — protocols section, FEPs section, then detailed ActivityPub documentation — but neither uses a rigid template. They adapted the convention to their needs.

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5. Machine-Readable Discovery

Via NodeInfo 2.1

FEDERATION.md files can potentially be discovered automatically via NodeInfo 2.1's software.repository field, which points to the project's source code repository. A crawler could follow this link and look for FEDERATION.md at the repository root.

{
  "software": {
    "name": "mastodon",
    "version": "4.3.0",
    "repository": "https://github.com/mastodon/mastodon"
  }
}

From this, a tool can construct: https://github.com/mastodon/mastodon/blob/main/FEDERATION.md

Limitation

This approach requires the software.repository field (added in NodeInfo 2.1) and depends on the repository being publicly accessible. Many instances run forks or customized versions where the repository URL may not point to the right FEDERATION.md.

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6. The DOAP Companion: FEP-c893

FEP-c893 (by AvidSeeker, status DRAFT, received July 2024) proposes a doap.jsonld file as a machine-readable companion to FEDERATION.md.

What DOAP Provides

A JSON-LD file using the DOAP (Description of a Project) vocabulary:

{
  "@context": {
    "doap": "http://usefulinc.com/ns/doap#",
    "foaf": "http://xmlns.com/foaf/0.1/"
  },
  "@type": "doap:Project",
  "doap:name": "Example Server",
  "doap:homepage": "https://example.com",
  "doap:description": {
    "@language": "en",
    "@value": "A federated social media server"
  },
  "doap:implements": [
    "https://www.w3.org/TR/activitypub/",
    "https://webfinger.net/"
  ],
  "doap:supportedFEPs": [
    "https://codeberg.org/fediverse/fep/src/branch/main/fep/67ff/fep-67ff.md"
  ],
  "doap:maintainer": {
    "@type": "foaf:Person",
    "foaf:name": "Alice Developer"
  }
}

Key Fields

Field	Purpose
doap:name	Project name
doap:homepage	Project website
doap:description	Multilingual description
doap:repository	Repository URLs
doap:release	Version and date information
doap:implements	Federation protocols supported
doap:supportedFEPs	Adopted FEPs
doap:maintainer	Project maintainers

Relationship to FEP-67ff

FEP-c893 is the machine-readable counterpart to FEP-67ff's human-readable FEDERATION.md. Together they provide both developer documentation and automated capability discovery. This pairing was inspired by XMPP's XEP-0453, which uses the same DOAP vocabulary for capability reporting.

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7. Writing a FEDERATION.md

Step-by-Step Guide

1. Create the file at the root of your project repository

2. List supported protocols:

   • ActivityPub (specify Server-to-Server, Client-to-Server, or both)
   • WebFinger
   • HTTP Signatures (specify draft version)
   • NodeInfo (specify schema version)
   • Any other protocols (Diaspora, Zot, OStatus, etc.)

3. List supported FEPs with links to the FEP specifications

4. Document ActivityPub behavior — this is the most valuable section:

   • What Activity types your server sends and accepts
   • What Object types your server creates and understands
   • How inbox processing works for each Activity type
   • Non-standard extensions or properties your server uses
   • Known interoperability issues with specific implementations

5. Document addressing and delivery:

   • How public/followers-only/direct addressing works
   • Shared inbox support
   • Relay support

6. Note known limitations:

   • Activity types that are silently ignored
   • Content types that receive degraded display
   • Extension requirements for full interoperability

Best Practices

• Keep it updated — outdated documentation is worse than no documentation, because it misleads implementers
• Be specific about non-standard behavior — if your server requires something not in the ActivityPub spec (like Mastodon's HTTP Signature requirements), document it prominently
• Include wire-format examples — JSON examples of actual activities your server sends and expects are more useful than prose descriptions
• Document what you ignore — knowing that a server silently drops Like activities (like Lemmy does with standard Likes) saves implementers debugging time

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8. Origin and History

Darius Kazemi's 2020 Proposal

In January 2020, Darius Kazemi (creator of gath.io, a federated event organizing service, and Fellow at the Berkman Klein Center for Internet & Society) proposed FEDERATION.md on SocialHub. He had been implementing federation for gath.io and felt implementers needed better documentation on server behavior.

His original FEDERATION.md had three sections:

1. Federation philosophy
2. Inbox behavior (what the server does when receiving various activities)
3. Web application-triggered activities (what the server sends in response to user actions)

Early Adoption Timeline

Date	Event
January 5, 2020	Darius Kazemi proposes FEDERATION.md on SocialHub
January 9, 2020	WriteFreely becomes first adopter
February 4, 2020	Zot (Hubzilla family) adopts
February 8, 2020	Discussed at W3C Social CG meeting
March–October 2020	tavern, Smithereen, Lemmy adopt
April 2023	silverpill proposes FEP-67ff (~12 implementations)
September 5, 2023	FEP-67ff received as DRAFT
September 22, 2024	FEP-67ff achieves FINAL status
Present	40+ implementations

Key Observation

The convention grew organically for over 3 years before being formalized as a FEP. This "convention first, spec second" approach means FEP-67ff codified existing practice rather than inventing new requirements — a pattern that contributed to its successful adoption and FINAL status.

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9. Implementations

Over 40 projects have adopted FEDERATION.md, including:

Project	Category
Mastodon	Microblogging
Pleroma / Akkoma	Microblogging
GoToSocial	Microblogging
Pixelfed	Photo sharing
PeerTube	Video sharing
Lemmy	Link aggregation
BookWyrm	Book reviews
WriteFreely	Long-form writing
Friendica	Social networking
Hubzilla	Social networking
Funkwhale	Music sharing
WordPress ActivityPub	Blogging plugin
Mitra	Microblogging
Smithereen	Social networking
Bonfire	Social networking

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10. Capability Discovery Landscape

FEDERATION.md addresses documentation but not machine-readable discovery. Several other FEPs tackle the machine-readable side:

FEP	Approach	Machine-readable?	Status
FEP-67ff	FEDERATION.md documentation	No (human only)	FINAL
FEP-c893	DOAP JSON-LD companion file	Yes	DRAFT
FEP-6481	IRI list in NodeInfo metadata	Yes	WITHDRAWN
FEP-9fde	Reverse-FQDN operations in NodeInfo	Yes	DRAFT
FEP-eb22	Type lists in NodeInfo	Yes	DRAFT
FEP-844e	Capability URIs on AP actors	Yes	DRAFT

FEP-67ff is the only capability-related FEP to reach FINAL status. Its success is partly because it focused on the simplest possible requirement (a Markdown file) rather than trying to solve machine-readable discovery.

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11. Known Issues

• No standard structure — every project formats their FEDERATION.md differently, making automated parsing impossible. This is by design (the spec explicitly allows arbitrary structure) but limits tooling.
• Freshness problem — there is no mechanism to verify whether a FEDERATION.md is up-to-date. Some files document features from years ago that may have changed.
• Discovery gap — finding a project's FEDERATION.md requires knowing the repository URL. NodeInfo 2.1's software.repository field helps but is not universally implemented.
• No machine-readable companion at scale — FEP-c893 (DOAP) exists as a DRAFT but has limited adoption. The Murmurations protocol was proposed as an alternative in 2021 but was not adopted.
• Fork divergence — many Fediverse instances run forks or customized versions. The upstream FEDERATION.md may not accurately describe a particular instance's behavior.