| 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
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
