kb-mbin

name	kb-mbin
description	Background knowledge about Mbin, the federated content aggregator and microblogging platform (active community fork of Kbin). Covers the hybrid dual content model (threads as Page + microblogs as Note in one platform), magazines as Group actors with Announce relay, the three actor types (Application instance actor at /i/actor, Person user at /u/username, Group magazine at /m/name), the full activity reference (Create, Update, Delete, Like, Dislike, Announce, Follow, Accept, Block, Flag, Lock, Add, Remove), the voting system (Like for upvotes, Dislike for downvotes with historical federation issues, Announce for boosts — boosts and votes are separate unlike Lemmy), the hybrid thread+microblog model and why it enables superior Mastodon integration, the tech stack (PHP 8.3+/Symfony 7.4/ PostgreSQL/RabbitMQ/Redis, AGPL-3.0), the async message processing architecture (Symfony Messenger with 15 inbox + 15 outbox message types), the REST API with OAuth2 and Swagger docs, the Mbin fork history (forked from Kbin October 2023 by Melroy van den Berg after creator Ernest Wisniewski's prolonged absences, C4 collective governance), codebase structure (106 entity classes, 33 src directories), deployment model (Docker or bare metal, 4+ vCPU/6GB+ RAM), moderation tools (magazine-level and instance-level bans, CLI admin commands, federated ban propagation), Mbin vs Lemmy comparison (Mbin has microblogging + user-following + separate boost/vote, Lemmy has more apps and users), and federation interoperability details including the @context with ostatus/toot/pt/lemmy namespaces. Load when the user asks about Mbin specifically; implementing an Mbin-compatible ActivityPub server; how Mbin's hybrid thread+microblog model works; how Mbin magazines federate as Group actors; how Mbin voting and boosting work; Mbin's async message processing architecture; the Mbin fork from Kbin and C4 governance; Mbin deployment and administration; Mbin moderation and CLI commands; how Mbin differs from Lemmy or Kbin; interoperating with Mbin instances; or building software that federates with Mbin.
user-invocable	false

Mbin — Complete Reference

Overview

Mbin is a federated content aggregator and microblogging platform for the Fediverse — a Reddit + Mastodon hybrid. It is the active community fork of Kbin, created by Melroy van den Berg on October 21, 2023 (first release v1.0.0 on October 30, 2023) after Kbin's sole developer Ernest Wisniewski became unable to maintain the project.

Mbin's key differentiator is its hybrid dual content model: it combines Reddit-style link aggregation (threads organized into magazines) and Mastodon-style microblogging (short-form posts) in a single platform. This enables significantly better Mastodon integration than Lemmy or PieFed.

Governed under the Collective Code Construction Contract (C4) — no single maintainer, consensus-based on Matrix, any maintainer can merge PRs. 35 releases, 4,477 commits, 30+ contributors as of early 2026. Licensed AGPL-3.0. Built with PHP 8.3+/Symfony 7.4/PostgreSQL.

---

1. Technology Stack

Component	Technology
Backend	PHP 8.3+ (8.4 recommended)
Framework	Symfony 7.4.x
ORM	Doctrine 2.19.6
Database	PostgreSQL (14–18)
Message queue	RabbitMQ (with optional AMQProxy for connection pooling)
Cache	Redis / Valkey / KeyDB
Real-time	Mercure (optional, server-sent events)
Frontend	Twig templates (9.4%), SCSS (2.5%), JavaScript (1.6%)
Bundler	Webpack
Web server	Nginx, Apache, or Caddy
Image processing	GD with blurhash support
Object storage	Local filesystem or S3 (AWS, MinIO, Ceph)
Deployment	Docker (Debian Trixie base) or bare metal
License	AGPL-3.0
Documentation	Docusaurus (docs.joinmbin.org)

Language Breakdown

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

Key Dependencies

• Symfony 7.4 (framework-bundle, security-bundle, twig-bundle, messenger)
• Doctrine ORM + Migrations
• OAuth2 providers: Facebook, GitHub, Google, Keycloak, Discord, Azure
• TOTP-based two-factor authentication
• AWS S3 SDK, blurhash, web push notifications, JWT via phpseclib
• swagger-php for API documentation
• PHPUnit + Paratest (parallel testing), PHPStan (static analysis)

---

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. Magazines are represented as ActivityPub Group actors at /m/name.

The Hybrid Dual Content Model

This is Mbin's defining feature. Two content types coexist within each magazine:

Type	Description	AP Object	Entity Class
Thread (Entry)	Links, articles, discussion posts with titles	Page	Entry + EntryComment
Microblog (Post)	Short-form posts (like Mastodon)	Note	Post + PostComment
Comment	Replies to threads or microblogs	Note (with inReplyTo)	EntryComment or PostComment
Private message	Direct messages between users	ChatMessage	—

Why this matters for federation: Lemmy and PieFed only see Mastodon posts that users intentionally tag to appear on the Threadiverse. Mbin's microblog section can follow Mastodon users directly, display their posts in the microblog view, and federate mentions bidirectionally. This makes Mbin the strongest Threadiverse bridge to the microblogging Fediverse.

Navigation Structure

The UI reflects the hybrid model with tabs: Combined, Threads, Microblog, People, Magazines. The combined view (v1.9.0+) shows threads and microblogs together as the default homepage.

Voting and Boosting

• Upvote — federated as Like activity (equivalent to Mastodon favourite)
• Downvote — federated as Dislike activity (historically had federation issues inherited from Kbin)
• Boost — federated as Announce activity (separate from voting)

Critical difference from Lemmy: In Mbin, boosting and voting are separate functions. In Lemmy, upvoting a post effectively boosts it. In Mbin, you can upvote without boosting and vice versa.

• Upvotes and boosts are public (visible to everyone)
• Downvotes are NOT public (to prevent harassment)
• Boosting elevates a post to the top of "Active" list and adds points for the "Hot" section

Entity classes: Vote, EntryVote, EntryCommentVote, PostVote, PostCommentVote. Favourites are separate: Favourite, EntryFavourite, EntryCommentFavourite, PostFavourite, PostCommentFavourite.

---

3. ActivityPub Implementation

Actor Types

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

JSON-LD Context

All payloads include a @context resolving to https://instance.example/contexts which maps multiple namespaces:

• ActivityStreams (https://www.w3.org/ns/activitystreams)
• W3C Security vocabulary
• ostatus
• schema.org
• toot (Mastodon extensions)
• pt (PeerTube extensions)
• lemmy (Lemmy extensions)

Discovery Protocols

Protocol	Endpoint	Source File
WebFinger	/.well-known/webfinger	WebFingerController.php + Service/ActivityPub/Webfinger/
NodeInfo	/.well-known/nodeinfo	NodeInfoController.php
Host-Meta	/.well-known/host-meta	HostMetaController.php

Shared Inbox

/f/inbox for instance-wide activity delivery.

HTTP Signatures

• Implementation: src/Service/ActivityPub/HttpSignature.php
• Validation: src/Service/ActivityPub/SignatureValidator.php
• Key generation: src/Service/ActivityPub/KeysGenerator.php
• Private key rotation via CLI: mbin:user:private-keys:rotate
• After rotation, other instances take up to 24 hours to update stored keys

---

4. ActivityPub Object Types and 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"],
  "audience": "https://instance.example/m/magazine",
  "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,
  "tag": [
    {"type": "Hashtag", "name": "#fediverse", "href": "https://instance.example/tag/fediverse"}
  ]
}

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"],
  "cc": ["https://instance.example/m/magazine/followers"],
  "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",
  "to": ["https://www.w3.org/ns/activitystreams#Public"],
  "cc": ["https://instance.example/m/magazine/followers"],
  "content": "<p>Reply text</p>",
  "source": {
    "content": "Reply text",
    "mediaType": "text/markdown"
  },
  "tag": [
    {"type": "Mention", "href": "https://instance.example/u/alice", "name": "@alice"}
  ]
}

Vote (Like/Dislike)

{
  "type": "Like",
  "id": "https://instance.example/u/alice/like/456",
  "actor": "https://instance.example/u/alice",
  "object": "https://other.example/m/magazine/t/12345",
  "to": ["https://other.example/m/magazine"]
}

Like activities use the magazine ID in the to field (changed in v1.9.1 from using the followers collection).

Collection Endpoints

Collection	Type	Description
Outbox	OrderedCollection	Create activities, paginated with first
Followers	OrderedCollection	Users: individual refs; Magazines: counts only
Following	OrderedCollection	Users only
Moderators	OrderedCollection	Non-paginated list of moderator URIs
Featured	OrderedCollection	Non-paginated pinned threads

---

5. Activity Reference

Content Activities

Activity	Purpose
Create	Create threads, microblogs, comments, messages
Update	Edit content or account profiles
Delete	Remove content/accounts, replaced with Tombstone; optional removeData flag
Lock	Disable comments on threads/microblogs

Social Activities

Activity	Purpose
Follow	Subscribe to user or magazine
Accept / Reject	Follow request responses (auto-sent on Follow receipt)
Undo	Reverse Follow, Like, Dislike, or Announce
Like	Upvote
Dislike	Downvote
Announce	Boost/reshare; also magazine relay wrapping

Moderation Activities

Activity	Purpose
Block	Ban user from magazine or instance (optional expiration)
Flag	Report content (distributed only to instances hosting magazine moderators)
Add / Remove	Moderator assignment and thread pinning to target collections

Magazine Announcements

Magazines Announce user activities to followers. The full set of announced activities: Create, Update, Add, Remove, Announce, Delete, Like, Dislike, Flag, Lock. Flag announcements are restricted to instances hosting the magazine's moderators.

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

---

6. Async Message Processing Architecture

Mbin uses Symfony Messenger with RabbitMQ (Redis fallback) for asynchronous processing of all federation messages.

Incoming Inbox Message Types (15)

ActivityMessage, AddMessage, AnnounceMessage, BlockMessage, ChainActivityMessage, CreateMessage, DeleteMessage, DislikeMessage, EntryPinMessage, FlagMessage, FollowMessage, LikeMessage, LockMessage, RemoveMessage, UpdateMessage

Outgoing Outbox Message Types (15)

AddMessage, AnnounceLikeMessage, AnnounceMessage, BlockMessage, CreateMessage, DeleteMessage, DeliverMessage, EntryPinMessage, FlagMessage, FollowMessage, GenericAnnounceMessage, LikeMessage, LockMessage, RemoveMessage, UpdateMessage

Worker Configuration

php bin/console messenger:consume scheduler_default old async \
  outbox deliver inbox resolve receive failed --time-limit=3600

Recommended: 6 Supervisor worker processes, running as www-data.

AMQProxy

Optional AMQP connection pooling proxy (port 5673) that reduces TCP connection overhead by reusing RabbitMQ channels.

---

7. Magazine (Group) Federation Details

Magazines are the core organizational unit and federate identically to Lemmy communities: as Group actors using the Announce relay pattern.

Magazine Features

• Any user can create a magazine and becomes its owner
• Owners appoint moderators with Add/Remove to /moderators collection
• Custom CSS per magazine (local display only, does not federate)
• Magazine banners compatible with Lemmy community banners (v1.9.0+)
• Magazine tags — moderators set hashtags that route matching microblogs into the magazine
• Pinned content via featured collection
• Discoverable flag controls search visibility
• Indexable flag controls robots.txt advisory

Magazine Rules Deprecation

The magazine rules field is deprecated — rules cannot be properly federated to other servers. The workaround appends rules to the magazine description with a ### Rules header.

Entity Classes

Magazine, MagazineBan, MagazineBlock, MagazineLog (15+ specialized subclasses), MagazineOwnershipRequest, MagazineSubscription, MagazineSubscriptionRequest, Moderator, ModeratorRequest

---

8. REST API

REST API with Swagger/OpenAPI documentation generated via swagger-php.

Authentication

OAuth2 with RSA key pair:

• Private key: openssl genrsa -des3 -out ./config/oauth2/private.pem 4096
• Environment variables: OAUTH_PRIVATE_KEY, OAUTH_PUBLIC_KEY, OAUTH_ENCRYPTION_KEY
• External SSO via Facebook, GitHub, Google, Keycloak, Discord, Azure

API Resource Groups (12)

Bookmark, Combined, Domain, Entry, Instance, Magazine, Message, Notification, OAuth2, Post, Search, User

Key Endpoints

• /api/instance/settings — instance configuration
• /api/instance/ban, /api/instance/unban — instance-level bans
• Thread and microblog locking endpoints (v1.9.1+)
• Entry/post CRUD with image upload support

---

9. Moderation Tools

Magazine-Level

• Owners appoint moderators
• Moderators can: pin/unpin threads, ban/unban users, lock/unlock content, delete/restore content, add/remove other moderators
• Public moderation logs with type filtering (v1.9.0+)
• Moderator assignments federate via Add/Remove activities

Instance-Level

• Global moderators view, approve, or deny account signups (MBIN_NEW_USERS_NEED_APPROVAL, default: false)
• Federation allow list (MBIN_USE_FEDERATION_ALLOW_LIST, default: false)
• Instance-wide user blocking via Block activities
• Federated bans — both incoming and outgoing (v1.9.0+)

CLI Admin Commands

Command	Purpose
mbin:user:create	Create users with optional admin/moderator privileges
mbin:user:admin	Grant/revoke admin privileges
mbin:user:delete	Delete user and notify fediverse
mbin:user:moderator	Grant/revoke global moderator
mbin:user:verify	Activate/deactivate users (bypasses email verification)
mbin:user:password	Reset passwords
mbin:user:private-keys:rotate	Rotate federation authentication keys
mbin:magazine:create	Create/remove/purge magazines
mbin:messages:remove_and_ban	Search DMs, ban senders, remove messages
mbin:check:duplicates-users-magazines	Find/remove duplicate accounts
mbin:ap:actor:update	Update remote users and avatars
mbin:ap:import	Import ActivityPub resources by URL

Anti-Abuse

• Anubis DDoS protection integration (v1.9.0+)
• robots.txt blocks for vote, boost, report, crosspost, and search paths
• Per-user and per-magazine discoverable/indexable settings

---

10. Deployment

Hardware Requirements

Resource	Minimum	Recommended
vCPU	4 cores (≥2GHz)	12 cores
RAM	6 GB	32 GB
Storage	40 GB	—

Docker Deployment

• Pre-built image: ghcr.io/mbinorg/mbin
• Base image: Debian Trixie, Node.js v24
• Built-in Caddy web server for automatic HTTPS
• Services: PHP app, Messenger worker, PostgreSQL, RabbitMQ, Valkey, Caddy
• Volumes: caddy_config, caddy_data, media, messenger_logs, oauth, php_logs, postgres, rabbitmq_data, rabbitmq_logs

Bare Metal

• OS: Debian 12+ or Ubuntu 22.04 LTS+
• PHP-FPM: pm.max_children=70, pm.start_servers=10
• PHP config: max_execution_time=60, upload_max_filesize=12M, memory_limit=512M
• OPCache: opcache.memory_consumption=512, opcache.jit=1255, preload enabled
• Node.js 22+ required for frontend asset building
• Supervisor for worker process management
• Installation root: /var/www/mbin

---

11. Codebase Structure

Top-Level src/ Directories (33)

ActivityPub/           Command/              Controller/
DTO/                   DataFixtures/         DoctrineExtensions/
Document/              Entity/ (106 classes) Enums/
Event/                 EventListener/        EventSubscriber/
Exception/             Factory/              Feed/
Form/                  Kernel.php            Markdown/
Message/               MessageHandler/       Middleware/
PageView/              Pagination/           Payloads/
Provider/              Repository/           Scheduler/
Schema/                Security/             Service/ (48 items)
Twig/                  Utils/                Validator/

ActivityPub Controllers (14 files + 2 subdirectories)

ContextsController, EntryCommentController, EntryController, HostMetaController, InstanceController, InstanceOutboxController, MessageController, NodeInfoController, ObjectController, PostCommentController, PostController, ReportController, SharedInboxController, WebFingerController + Magazine/ + User/

Service Layer Key Classes

ActivityPubManager, ApHttpClient, HttpSignature, KeysGenerator, SignatureValidator, Note, Page, MarkdownConverter, DeliverManager, EntryManager, PostManager, MagazineManager, UserManager, VoteManager, FavouriteManager, BookmarkManager, ReportManager, ReputationManager, TagManager, MentionManager, SearchManager, FeedManager, ImageManager

---

12. Mbin vs Lemmy

Aspect	Mbin	Lemmy
Language	PHP 8.3+ (Symfony)	Rust (Actix-web)
Content types	Threads + Microblogs	Threads only
Communities	"Magazines" (Group)	"Communities" (Group)
AP objects	Page (threads) + Note (microblogs)	Page only
Mastodon integration	Strong — microblog section shows Mastodon content	Limited
User following	Yes — can follow individual accounts	No — communities only
Boost vs vote	Separate functions	Combined (upvote = boost)
Downvote federation	Dislike (historical issues)	Dislike (reliable)
Mention federation	Strong (bidirectional with Mastodon)	Weaker
Third-party apps	Limited (Interstellar)	Many (Boost, Thunder, Voyager)
Governance	C4 collective, multiple maintainers	2 primary developers
Maturity	Newer (Oct 2023)	Older (Feb 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 Mbin and vice versa.

Key friction points:

• Mbin microblog Note posts appear as comments in Lemmy (Lemmy only understands Page for top-level posts)
• Lemmy combines upvoting and boosting; Mbin treats them separately
• Magazine banners are compatible with Lemmy community banners (v1.9.0+)
• Mbin's @context includes the lemmy namespace for compatibility

---

13. History and Governance

Kbin Background

Kbin was created by Ernest Wisniewski (Polish developer), with development starting January 2021 and kbin.social launching April 2023. During the Reddit API crisis (June 2023), kbin.social grew from ~300 to 30,000+ users in one week, eventually reaching 123,000+.

Ernest experienced compounding personal crises (divorce, surgery, full-time job) and began disappearing for weeks to months. Pull requests on Codeberg sat unmerged. kbin.social went offline permanently.

The Fork

Melroy van den Berg (Dutch software engineer, DevOps architect) announced the Mbin fork on October 21, 2023. His stated motivation: "I saw the project slowly dying over the past months, and I couldn't let this happen."

The name "Mbin" = "M" (Melroy) + "bin" (from kbin). Melroy acknowledged: "I know, I wasn't creative."

Within one week, the community had already shipped GUI improvements, backend fixes, security patches, and documentation. After ~8-10 months, Mbin stopped porting Kbin code entirely — all subsequent development is original work.

C4 Governance

The Collective Code Construction Contract (from ZeroMQ/Pieter Hintjens):

• No single-maintainer bottleneck — multiple contributors hold org owner rights
• All maintainers peer-review each other's code
• PRs merged by any maintainer after consensus on Matrix
• "Bad actors" removed by public discussion and majority agreement
• Deliberately prevents the single-point-of-failure that killed Kbin

Release Timeline

Version	Date	Key Changes
v1.0.0	Oct 30, 2023	First release
v1.7.0	mid 2024	PeerTube support, DMs, push notifications
v1.8.4	Sep 7, 2024	Security patch, dead instance handling
v1.9.0	Dec 14, 2024	Combined homepage, magazine banners, federated bans, Symfony 7
v1.9.1	Feb 9, 2025	Thread/microblog locking, RSS improvements, faster search

---

14. Instances and Ecosystem

~18 instances, ~8,172 total users, ~750 monthly active users.

Instance	URL	Users	MAU
Fedia	fedia.io	6,036	488
kbin.earth	kbin.earth	770	131
the/brain/bin	thebrainbin.org	245	34
GehirnEimer	gehirneimer.de	136	28

Fedia.io dominates with ~74% of all users (concentration risk).

Mobile Apps

Interstellar is the primary mobile client (Android, iOS, Linux, Windows) — functional but limited compared to Lemmy-specific apps. The Threadiverse primer recommends Mbin only for desktop browsing.

A unified TypeScript client (github.com/aeharding/threadiverse) is in development for Lemmy, PieFed, and Mbin.

---

15. Common Implementation Mistakes

1. Sending Note objects to a magazine expecting thread display — Mbin uses Page for threads (entries) and Note for microblogs. A Note sent to a magazine appears in the microblog section, not as a thread. Use Page with a name (title) for thread-style posts.

2. Ignoring the separate boost/vote model — Unlike Lemmy where upvoting boosts, Mbin treats Like (upvote) and Announce (boost) as independent actions. Implement both if you want full interoperability.

3. Expecting downvotes to always federate — Mbin sends Dislike activities but historically had federation issues inherited from Kbin. Downvotes are not publicly visible on Mbin. Do not assume reliable Dislike delivery from older Mbin versions.

4. Not including the magazine in activity recipients — Activities targeting a magazine must include the magazine Group actor in to or cc. The magazine must receive the activity to Announce it to followers.

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

6. Ignoring source with markdown — All content preserves original markdown in the source field alongside HTML in content. Prefer rendering from source if you want accurate markdown.

7. Not handling both Page and Note from the same magazine — A single magazine may produce both Page (threads) and Note (microblogs) objects. Consuming software must handle both types from the same Group actor.

8. Expecting Like activities to use followers collection in to — As of v1.9.1, Like/Dislike activities use the magazine ID in the to field instead of the followers collection.

9. Treating magazine rules as a reliable field — The rules field is deprecated and cannot federate. Rules are embedded in the magazine description under a ### Rules header instead.

10. Not accepting application/json content type — Mbin accepts both application/activity+json and plain application/json on all ActivityPub endpoints, and may send requests with application/json. Strict content-type checking will break interoperability.