kb-kbin

name	kb-kbin
description	Background knowledge about Kbin and its active community fork Mbin, the decentralized content aggregator and microblogging platform for the Fediverse (Reddit + Mastodon hybrid). Covers the dual content model (threads/link aggregation via Page objects + microblogging via Note objects in a single platform), magazines as Group actors with Announce relay (same pattern as Lemmy communities), the three actor types (Application instance actor at /i/actor, Person user at /u/username, Group magazine at /m/name), supported activities (Follow, Like, Announce, Create, Update, Delete, Block, Flag, Lock, Add, Remove), the critical detail that downvotes do NOT federate, content object mapping (threads as Page, microblogs as Note, comments as Note with inReplyTo, private messages as ChatMessage), the tech stack (PHP 8.2+/Symfony/PostgreSQL/RabbitMQ/Redis, AGPL-3.0), the REST API with OAuth2 and Swagger docs at /api/docs, the Mbin fork history (Kbin discontinued after creator Ernest Wisniewski's absences, Mbin forked October 2023 with C4 governance, improved federation/performance/ scaling), Kbin vs Lemmy comparison (Kbin has microblogging + threads while Lemmy is threads only, Kbin has stronger Mastodon integration, Lemmy federates downvotes while Kbin does not), the Threadiverse ecosystem context (Lemmy, Mbin, PieFed, Sublinks), voting/reputation system (reputation is cosmetic only), and federation interoperability details. Load when the user asks about Kbin or Mbin; implementing a Kbin/Mbin-compatible ActivityPub server; how Kbin magazines federate as Group actors; how Kbin combines link aggregation and microblogging; why Kbin downvotes don't federate; the Kbin to Mbin transition; how Kbin/Mbin differs from Lemmy; interoperating with Kbin/Mbin instances; the Threadiverse; or building software that federates with Kbin/Mbin.
user-invocable	false

Kbin / Mbin — Complete Reference

Overview

Kbin (stylized /kbin) was a decentralized content aggregator and microblogging platform for the Fediverse — a Reddit + Mastodon hybrid. Created by Ernest Wiśniewski (Polish developer) with development becoming serious in early 2023, the flagship instance kbin.social launched in April 2023. The project received NLnet funding (NGI0 Entrust Fund, December 2022).

Kbin is now discontinued. Its active community fork Mbin (founded October 2023 by Melroy van den Berg) continues development with significant improvements to federation, performance, and governance. When this document says "Kbin/Mbin," the information applies to both; Mbin-specific features are noted.

Kbin's key differentiator from Lemmy: it combines two content models in one platform — Reddit-style link aggregation (threads organized into magazines) and Mastodon-style microblogging (short-form posts). This dual nature enables stronger integration with microblogging platforms like Mastodon.

Licensed AGPL-3.0. Built with PHP/Symfony/PostgreSQL.

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1. Technology Stack

Component	Technology
Backend	PHP 8.2+
Framework	Symfony
Database	PostgreSQL
Message queue	RabbitMQ
Cache	Redis / KeyDB / Valkey
Real-time	Mercure (optional)
Frontend	Twig templates, SCSS, JavaScript
Image processing	GD or ImageMagick
Web server	Nginx, Apache, or Caddy
Deployment	Docker / Docker Compose
License	AGPL-3.0

Language Breakdown

• PHP: 86.3%
• Twig: 9.4%
• SCSS: 2.5%
• JavaScript: 1.6%

Development Tools

• PHPUnit (testing), PHPStan (static analysis), Psalm (security scanning), Composer (dependencies), API Platform (API generation)

---

2. Content Model

Magazines

The primary organizational unit — equivalent to subreddits (Reddit), communities (Lemmy), or topics (PieFed). Any registered user can create a magazine and automatically becomes its owner with administrative tools including moderator appointment.

Content Types

Type	Description	AP Object
Thread (link)	External links and articles with titles	Page
Thread (text)	Self-text discussion posts with titles	Page
Microblog	Short-form posts (like Mastodon)	Note
Comment	Replies to threads or microblogs	Note (with inReplyTo)
Private message	Direct messages between users	ChatMessage (custom)

The dual content model is what distinguishes Kbin/Mbin from Lemmy. Threads work like Reddit posts (link or self-text with a title, displayed in a list). Microblogs work like Mastodon posts (short-form, displayed in a stream). Both coexist within each magazine.

Voting

• Upvote — positive engagement, federated as Like activity
• Downvote ("Reduce") — negative engagement, local only — does NOT federate
• Boost — reshare/reblog, federated as Announce activity

The non-federation of downvotes is a critical interoperability detail. Lemmy federates downvotes via Dislike; Kbin/Mbin does not send them. Downvotes from Kbin/Mbin users are only visible on the local instance.

Reputation

Users accumulate reputation points from boosts and favourites on their content. Reputation is cosmetic only — visible on profile pages but has no functional effect (does not gate features or permissions).

Content Organization

• Follow magazines, users, or entire domains
• Block users, magazines, or domains
• Content categorized by tags and labels
• RSS feeds for threads, microblogs, or combined

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3. ActivityPub Implementation

Actor Types

Actor	Type	Path	Purpose
Instance	Application	/i/actor	Server-level actor, signs requests, inbox/outbox
User	Person	/u/username	Individual accounts with followers/following
Magazine	Group	/m/name	Community container, announces user activities

JSON-LD Context

The @context resolves to ActivityStreams, W3C security vocabulary, and custom namespaces including ostatus, schema.org, Mastodon extensions (toot:), PeerTube extensions, and Lemmy extensions.

Magazine (Group) Federation

Magazines use the same Group actor Announce relay pattern as Lemmy communities. When a user creates a thread in a magazine, the magazine's Group actor wraps the activity in an Announce and distributes it to all followers:

User creates thread → Create{Page} sent to Magazine
Magazine wraps → Announce{Create{Page}} sent to all followers
Remote instances receive Announce → display thread in magazine

This means subscribing to a magazine is a Follow sent to the Group actor. The Group actor then relays all content via Announce.

Activities Reference

Activity	Purpose
Follow	Subscribe to user or magazine
Accept / Reject	Follow request responses
Create	Create threads, microblogs, comments
Update	Edit content
Delete	Remove content
Like	Upvote (no Dislike — downvotes are local only)
Announce	Boost/reshare; also magazine relay wrapping
Undo	Reverse Like, Follow, or Announce
Block	Ban user (optional expiration timestamp, magazine-level or instance-level)
Flag	Report content (sent to magazine moderators' instances only)
Add / Remove	Moderator assignment, thread pinning
Lock	Lock threads/microblogs to prevent responses (Mbin)

Content Object Wire Format

Thread (Page):

{
  "type": "Page",
  "id": "https://instance.example/m/magazine/t/12345",
  "attributedTo": "https://instance.example/u/alice",
  "to": ["https://www.w3.org/ns/activitystreams#Public"],
  "cc": ["https://instance.example/m/magazine/followers"],
  "name": "Thread title",
  "content": "<p>HTML body</p>",
  "mediaType": "text/html",
  "source": {
    "content": "Markdown body",
    "mediaType": "text/markdown"
  },
  "inReplyTo": null,
  "sensitive": false,
  "stickied": false,
  "commentsEnabled": true
}

Microblog (Note):

{
  "type": "Note",
  "id": "https://instance.example/m/magazine/p/67890",
  "attributedTo": "https://instance.example/u/alice",
  "to": ["https://www.w3.org/ns/activitystreams#Public"],
  "content": "<p>Short-form post content</p>",
  "source": {
    "content": "Short-form post content",
    "mediaType": "text/markdown"
  },
  "tag": [
    {"type": "Hashtag", "name": "#fediverse"}
  ]
}

Comment (Note with inReplyTo):

{
  "type": "Note",
  "id": "https://instance.example/m/magazine/t/12345/-/comment/99",
  "attributedTo": "https://instance.example/u/bob",
  "inReplyTo": "https://instance.example/m/magazine/t/12345",
  "content": "<p>Reply text</p>",
  "source": {
    "content": "Reply text",
    "mediaType": "text/markdown"
  }
}

Key Federation Details

• Downvotes do NOT federate — only Like (upvote) and Announce (boost) are sent. No Dislike activity.
• Reports (Flag) are sent exclusively to instances housing the magazine's moderators.
• Bans (Block) include optional expiration timestamps and specify scope (magazine-level vs instance-level).
• Content includes focal point metadata and blurhash via Mastodon extensions.
• Supports all ActivityPub Actor Types including Service for bot/robot accounts.
• Accepts application/json headers across all ActivityPub endpoints (not just application/activity+json).
• All content preserves markdown source alongside HTML rendering.
• Multi-language content mapping supported.

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4. API

REST API with Swagger/OpenAPI documentation at /api/docs on each instance.

Authentication

OAuth2-based:

1. Register client: POST /api/client → returns identifier and secret
2. Request token → returns Bearer token, expiration, refresh token
3. Include Authorization: Bearer <token> on requests

Scopes

Scope	Access
read	Retrieve threads, view favorites
write	All modification operations

---

5. Kbin vs Lemmy

Aspect	Kbin/Mbin	Lemmy
Language	PHP (Symfony)	Rust (Actix-web)
Content types	Threads + Microblogs	Threads only
Communities	"Magazines"	"Communities"
AP object (posts)	Page (threads) + Note (microblogs)	Page only
Mastodon integration	Strong — microblog section shows Mastodon content	Limited
Downvote federation	No (local only)	Yes (Dislike activity)
Mention federation	Better (Mbin)	Weaker
PeerTube integration	Direct channel following (Mbin v1.7+)	Limited
Third-party apps	Very limited	Many (Jerboa, Thunder, Voyager)
Governance	Community-driven (Mbin)	Lemmy team (2 primary devs)
Maturity	Newer (2023)	Older (2019)

Interoperability

Both use Group actors for communities/magazines and Page objects for threads. They federate with each other: Lemmy communities appear as magazines in Kbin/Mbin and vice versa. Comments federate as Note objects with inReplyTo.

Key friction points:

• Lemmy sends Dislike for downvotes; Kbin/Mbin ignores them (or had historical display issues)
• Kbin/Mbin microblog Note posts appear as comments in Lemmy (since Lemmy only understands Page for top-level posts)
• Mention federation works better from Mbin than from Lemmy

---

6. History and the Mbin Fork

Kbin Timeline

Date	Event
Dec 2022	NLnet grant funding begins
Early 2023	Project moves to Codeberg, development accelerates
Apr 2023	kbin.social launches with a few hundred users
Jun 2023	Reddit API crisis — kbin.social grows from 300 to 30,000+ users in one week
Jun 2023	Emergency infrastructure: Fastly caching, Cloudflare, server upgrades
Late 2023	Ernest begins pattern of weeks-to-months-long absences
Oct 2023	Mbin fork created on GitHub
2024	kbin.social increasingly unstable, Ernest cites medical issues
Jun 2024	Ernest promises instance handover, then goes silent again
Sep 2024	kbin.social effectively ceases operation
Present	Kbin discontinued; Mbin is the active continuation

Mbin

Founded: October 12, 2023, by Melroy van den Berg.

Governance: Uses the Collective Code Construction Contract (C4) — no single-maintainer bottleneck. Multiple contributors have owner rights. Pull requests merged by any maintainer with community consensus on Matrix.

Key improvements over Kbin:

1. Federation compatibility — major fixes to interoperability issues
2. Performance and scaling — database optimizations, reduced background request overhead
3. Security — up-to-date dependencies, security-first patching
4. Documentation — hosted at docs.joinmbin.org
5. Thread/microblog locking
6. Discoverability and indexability settings
7. PeerTube channel following (since v1.7)
8. All ActivityPub Actor Types including Service for bots
9. Combined thread creation form (unified link/text/photo)

Current version: v1.9.1 (February 2026). 35 releases, 4,477 commits, 35+ contributors.

Around 8–10 months after forking, Mbin stopped porting Kbin code and focused on purely original development.

---

7. The Threadiverse Ecosystem

The "Threadiverse" is the link-aggregation / threaded-discussion portion of the Fediverse. All platforms interoperate via ActivityPub using Group actors for communities and Page/Note objects for content.

Software	Language	Status	Differentiator
Lemmy	Rust	Active	Most mature (2019), most users
Mbin	PHP	Active	Threads + microblogs combined
PieFed	Python	Active	Privacy-focused voting, rapid development
Sublinks	Java	In dev	Lemmy-compatible alternative backend
Lotide	Rust	Limited	Minimal, lightweight

---

8. Instances

Kbin Instances

8 tracked, mostly inactive or migrated to Mbin. kbin.social (flagship) is defunct.

Mbin Instances

23 tracked, almost all with >98% recent uptime:

• fedia.io — one of the largest, migrated from Kbin
• kbin.run — created due to kbin.social instability
• kbin.melroy.org — run by Mbin founder

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9. Interoperability Notes for Implementers

1. Threads arrive as Page objects — same as Lemmy. If your software handles Lemmy's Page posts, Kbin/Mbin threads will work the same way. Title is in name, body in content/source.

2. Microblogs arrive as Note objects — these are short-form posts without titles, identical in structure to Mastodon posts. They originate from a magazine but look like standard microblog posts. Lemmy displays these as comments since it only understands Page for top-level content.

3. No Dislike activity — Kbin/Mbin never sends downvotes over federation. If you receive a Like from a Kbin/Mbin instance, it's an upvote. You will never receive a Dislike. If your platform sends Dislike to a Kbin/Mbin instance, it may be ignored or cause display issues.

4. Magazines are Group actors — follow a magazine by sending Follow to the Group actor at /m/name. The magazine relays all content via Announce, identical to Lemmy communities.

5. ChatMessage for DMs — Kbin/Mbin uses a custom ChatMessage type for private messages, not standard Note with direct addressing. Other platforms may not understand this type.

6. Accepts application/json — Kbin/Mbin accepts both application/activity+json and plain application/json on all ActivityPub endpoints. No need to worry about content-type strictness.

7. Report routing — Flag activities are sent only to instances that host the magazine's moderators, not broadcast widely.

8. Ban expiration — Block activities can include expiration timestamps and scope (magazine-level vs instance-level). Handle the expiration field if present.

9. Reputation is cosmetic — Kbin/Mbin exposes reputation scores on user profiles, but these have no functional effect and should not be used for trust decisions.

10. Mastodon content in magazines — Kbin/Mbin's microblog section displays Mastodon posts matching magazine hashtags. This means Mastodon Note objects may appear alongside native Kbin/Mbin content in magazine feeds.