# Kb Kbin > 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 - Skill: `majiayu000/kb-kbin` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add majiayu000/kb-kbin` - Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/kb-kbin/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: majiayu000 (https://skillmd.com/u/majiayu000) - Updated: 2026-09-09 - Page: https://skillmd.com/skills/majiayu000/kb-kbin --- # 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. --- ## 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 --- ## 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):** ```json { "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": "

HTML body

", "mediaType": "text/html", "source": { "content": "Markdown body", "mediaType": "text/markdown" }, "inReplyTo": null, "sensitive": false, "stickied": false, "commentsEnabled": true } ``` **Microblog (Note):** ```json { "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": "

Short-form post content

", "source": { "content": "Short-form post content", "mediaType": "text/markdown" }, "tag": [ {"type": "Hashtag", "name": "#fediverse"} ] } ``` **Comment (Note with inReplyTo):** ```json { "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": "

Reply text

", "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. --- ## 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 ` 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 --- ## 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.