kb-misskey

name	kb-misskey
description	Background knowledge about Misskey, the Japanese-origin federated microblogging platform (created 2014 by syuilo). Covers Misskey's ActivityPub extensions (custom namespace https://misskey-hub.net/ns# with _misskey_content, _misskey_quote, _misskey_reaction for emoji reactions on Like activities, _misskey_votes, _misskey_talk for chat, isCat boolean, _misskey_followedMessage, _misskey_requireSigninToViewContents, _misskey_makeNotesFollowersOnlyBefore, _misskey_makeNotesHiddenBefore, _misskey_license), MFM (Misskey Flavored Markdown) proprietary markup with animations/colors/effects, emoji reactions as primary engagement mechanism (Unicode + custom emoji, federated via Like with _misskey_reaction), the Drive file management system, Antennas (custom filtered feeds), Deck UI, Channels, Pages, Clips, Plugins, Themes, Widgets, isCat mode, the tech stack (Node.js/TypeScript/NestJS/PostgreSQL/Redis/Vue.js 3/Vite, AGPL-3.0), REST API (POST-based) and WebSocket streaming API, Note visibility levels (public/home/followers/specified), the extensive fork ecosystem (Sharkey active soft fork, Cherrypick, Firefish/Calckey discontinued, Iceshrimp.NET C# rewrite, FoundKey EOL, Catodon discontinued, Meiskey), Misskey vs Mastodon comparison, and federation interoperability quirks. Load when the user asks about Misskey; implementing a Misskey-compatible ActivityPub server; Misskey's ActivityPub extensions and custom namespace; how emoji reactions federate from Misskey; the _misskey_reaction or _misskey_quote properties; MFM markup language; federating with Misskey instances; the Misskey fork ecosystem (Sharkey, Firefish, Iceshrimp, FoundKey); how Misskey differs from Mastodon; Misskey's Drive or Antenna features; or building software that interoperates with Misskey-family platforms.
user-invocable	false

Misskey — Complete Reference

Overview

Misskey is a free, open-source, decentralized microblogging platform — a feature-rich Japanese-origin Fediverse platform that predates many others. Created by syuilo (Eiji Shinoda) in 2014 as a BBS-style forum, it adopted ActivityPub in 2018. The name comes from the song "Brain Diver" by the band May'n. Licensed AGPL-3.0.

Misskey is explicitly not a Mastodon fork — it is "a project completely different from Mastodon or other alike projects." Its cultural DNA reflects Japanese social media preferences: emoji reactions as the primary engagement mechanism (not simple likes), rich visual formatting (MFM), integrated file management (Drive), and playful features like isCat mode and the mascot Ai (藍). Community members are called "Misskists."

As of late 2024: ~918,550 registered accounts, ~25,782 active users, 1,096+ instances. The flagship instance misskey.io is reportedly the second largest instance in the entire Fediverse. MisskeyHQ exists as a company entity, funded by donations and software licensing.

---

1. Technology Stack

Component	Technology
Backend	Node.js with TypeScript
Framework	NestJS (dependency injection)
Database	PostgreSQL (TypeORM)
Cache / Queue	Redis (ioredis) / BullMQ
Frontend	Vue.js 3 (Composition API, TypeScript)
Build tool	Vite
License	AGPL-3.0

Resource Footprint

Small instances: ~848 MB RAM with CPU bursts. A $10/month VPS suffices for small communities; $20/month for 15–50 users.

Repository

https://github.com/misskey-dev/misskey

---

2. ActivityPub Extensions

Misskey uses the JSON-LD namespace https://misskey-hub.net/ns# (prefix misskey). This is the most extensive set of custom ActivityPub extensions in the Fediverse ecosystem.

Extension Reference

Property	On	Description
_misskey_content	Note	Deprecated. MFM source text (equivalent to source property)
_misskey_summary	Actor	Actor summary in MFM format
_misskey_quote	Note	ID of quoted note. Compatible with fedibird:quoteUri and as:quoteUrl
_misskey_reaction	Like	Emoji reaction type. Unicode emoji or :name: custom emoji string
_misskey_votes	Question option	Vote count (equivalent to replies.totalItems)
_misskey_talk	Note	Boolean true marks note as a chat message
isCat	Actor	Boolean — actor identifies as a cat (triggers visual effects)
_misskey_followedMessage	Actor	Custom message on follow notification (since 2024.9.0-alpha.11)
_misskey_requireSigninToViewContents	Actor	Forbids display to non-signed-in viewers
_misskey_makeNotesFollowersOnlyBefore	Actor	Restricts past notes to followers only. Value: Unix epoch ms (negative = relative)
_misskey_makeNotesHiddenBefore	Actor	Hides past notes from all except author. Same value format
_misskey_license	Emoji	License metadata. Properties: freeText (string or null)

Emoji Reactions Wire Format

Misskey's emoji reactions are the most significant interoperability concern. When a user reacts with an emoji, Misskey sends a Like activity with _misskey_reaction set to the emoji:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://w3id.org/security/v1",
    {
      "misskey": "https://misskey-hub.net/ns#",
      "_misskey_reaction": "misskey:_misskey_reaction"
    }
  ],
  "type": "Like",
  "id": "https://misskey.example/likes/abc123",
  "actor": "https://misskey.example/users/alice",
  "object": "https://remote.example/notes/xyz",
  "_misskey_reaction": "👍",
  "content": "👍"
}

For custom emoji reactions:

{
  "type": "Like",
  "_misskey_reaction": ":blobcat:",
  "content": ":blobcat:",
  "tag": [
    {
      "type": "Emoji",
      "id": "https://misskey.example/emojis/blobcat",
      "name": ":blobcat:",
      "icon": {
        "type": "Image",
        "url": "https://misskey.example/files/blobcat.png"
      }
    }
  ]
}

Interoperability: Platforms that do not understand _misskey_reaction will treat these as standard Like activities (favourites). Custom emoji reactions are only visible to other Misskey-family software. The content field is also set to the reaction value as a fallback.

Quote Posts Wire Format

{
  "type": "Note",
  "id": "https://misskey.example/notes/abc123",
  "content": "<p>My thoughts on this</p>",
  "_misskey_quote": "https://remote.example/notes/original",
  "quoteUrl": "https://remote.example/notes/original"
}

Both _misskey_quote and quoteUrl are set for compatibility. Also recognized: https://fedibird.com/ns#quoteUri.

---

3. MFM (Misskey Flavored Markdown)

Proprietary markup language usable in notes, content warnings, usernames, and bios. General syntax: $[name.attribute1,attribute2=value content]

Text Formatting

• Bold: **text**
• Small: <small>text</small>
• Center: <center>text</center>
• Quotes: > text
• Ruby: $[ruby text reading]
• Links: [label](url)
• Code: backticks (inline), triple backticks with language (blocks, 200+ languages via Shiki)

Visual Effects

Syntax	Effect
$[flip text]	Horizontal/vertical flip
$[font.serif text]	Font change (serif, monospace, cursive, fantasy)
$[blur text]	Blur until hover
$[fg.color=hex text]	Foreground color
$[bg.color=hex text]	Background color
$[border.style=solid,width=4 text]	Border (solid, dotted, dashed, double, groove, ridge, inset, outset)
$[position.x=0.8,y=0.5 text]	Position shifting
$[rotate.deg=30 text]	Rotation
$[scale.x=4,y=2 text]	Scaling (also $[x2], $[x3], $[x4])

Animations

Syntax	Effect
$[jelly text]	Jiggles
$[tada text]	Celebration
$[jump text]	Bouncing
$[bounce text]	Elasticity
$[spin text]	Rotation (modifiers: .left, .alternate, .x, .y)
$[shake text]	Vibration
$[twitch text]	Random twitching
$[rainbow text]	Color cycling
$[sparkle text]	Shimmer

All animations support .speed=5s for timing control.

Federation note: MFM is rendered as HTML when federating via ActivityPub. The _misskey_content (deprecated) and source properties carry the original MFM source. Non-Misskey platforms see plain HTML with animations and effects stripped.

---

4. Note System

Visibility Levels

Level	Description
public	Visible to everyone, appears on all timelines
home	Visible to everyone but only appears on home timeline
followers	Only visible to followers
specified	Only visible to specified users (direct message)

Features

• Content Warning (CW): summary field hides content behind a toggle
• Renote: Boost/reblog (Announce activity)
• Quote Renote: Boost with added commentary (_misskey_quote)
• Polls: Question activity type with _misskey_votes for counts
• Reactions: Full emoji reactions (see Section 2)
• Mentions: @-mentions across the Fediverse
• Hashtags: Standard Hashtag tag type

Timelines

Timeline	Content
Home	Notes from followed users
Local	All public notes from the instance
Social (Hybrid)	Home + Local combined
Global	All known public notes including remote

---

5. Unique Features

Drive

Cloud storage system for managing uploaded files. Files can be organized into folders and reused across multiple notes without re-uploading. Each file retains metadata (type, size, hash). Drive capacity is configurable per-user by instance administrators via role policies.

Antennas

Customizable filtered feeds that collect notes matching set conditions (keywords, users, file attachments) in real time. Essentially continuous background searches. Antennas exclude the user's own posts.

Deck UI

Multi-column layout with side-by-side views for an information-dense interface. Users can arrange timeline columns, notification panels, and other widgets freely.

Channels

Topic-based note collections within an instance. Similar to forums or discussion threads organized by subject.

Pages

Static page creation system using MFM and custom emoji, enabling users to build content beyond notes.

Other Features

• Clips — public/private categorized bookmarks
• Plugins — extend web client functionality via AiScript
• Themes — full client appearance customization
• Widgets — small interactive dashboard displays
• Webhooks — external service integration
• Word mute / Thread mute — content filtering
• Charts — server data visualization
• Online status — activity indicators on profile icons
• Share form — at /share path for social sharing buttons
• Safe mode — disables custom CSS, plugins, themes
• Embeds — embed notes and timelines on external websites
• isCat mode — users identify as cats with visual effects in supporting clients

---

6. API

REST API

All endpoints use HTTP POST (not GET for reads):

POST /api/notes/create
POST /api/notes/show
POST /api/users/show
POST /api/following/create

Authentication via access tokens. SDK: misskey-js (TypeScript).

Streaming API

WebSocket-based with channel multiplexing:

{
  "type": "connect",
  "body": {
    "channel": "homeTimeline",
    "id": "arbitrary-unique-id"
  }
}

Available channels: globalTimeline, homeTimeline, hybridTimeline, localTimeline, main.

Multiple channels can be multiplexed on a single WebSocket connection using different IDs.

---

7. Fork Ecosystem

Misskey has the most extensive fork tree in the Fediverse. All forks federate with each other and the broader Fediverse.

Active Forks

Fork	Type	Key Differentiators
Sharkey	Soft fork (tracks upstream)	Federated note editing with history, Mastodon-compatible API + OAuth2, multi-platform import (Mastodon/Pleroma/Firefish/Twitter/Instagram/Facebook), GDPR data export, "Bubble" timeline, Argon2 hashing, multiple translation services
Cherrypick	Soft fork	Compatible with Misskey client ecosystem
Meiskey	v11 fork	Based on older Misskey v11

Discontinued / EOL Forks

Fork	Status	Notes
Firefish (was Calckey)	Discontinued 2024	Added recommended timeline, account migration, mobile-optimized UI. Lead developer became absent
Iceshrimp	Transitioning	JS version: security patches only. Iceshrimp.NET: complete C# rewrite (beta), Mastodon API support
FoundKey	End of Life	Hard fork of v12, goal was removing bloat
Catodon	Discontinued Nov 2025	Community-driven fork of Iceshrimp, created in reaction to Firefish governance failures

Fork Relationship

Misskey (syuilo, 2014–)
├── Sharkey (soft fork, ACTIVE)
├── Cherrypick (soft fork, ACTIVE)
├── Meiskey (v11 fork, ACTIVE)
├── FoundKey (v12 hard fork, EOL)
└── Calckey (2022) → Firefish (2023, DISCONTINUED)
    ├── Iceshrimp → Iceshrimp.NET (C# rewrite)
    └── Catodon (DISCONTINUED)

Pattern: Forks emerge from (a) feature gaps upstream won't fill, (b) governance/communication issues, or (c) architectural changes (Iceshrimp.NET's language rewrite).

---

8. Misskey vs Mastodon

Aspect	Misskey	Mastodon
Origin	Japan (2014)	Germany (2016)
Character limit	Configurable per instance	500 default
Reactions	Full emoji reactions (custom + Unicode)	Favourites only
File management	Built-in Drive	No persistent storage
Markup	MFM (animations, colors, effects)	Limited Markdown
Channels	Topic-based communities	No
Antennas	Custom filtered feeds	No equivalent
Resource usage	Lighter than Mastodon	Heavier
Mobile apps	Limited (PWA, third-party)	Official iOS/Android + many third-party
Post editing	Not in core (Sharkey has it)	Supported
User base	~918k (mostly Japanese)	~7.6M total

---

9. Interoperability Notes for Implementers

1. Emoji reactions arrive as Like activities — check for _misskey_reaction to distinguish a specific emoji reaction from a generic favourite. If absent, treat as a standard Like. The content field also contains the reaction value.

2. Custom emoji in reactions — when _misskey_reaction contains a :name: string, the tag array includes an Emoji object with the image URL. Display the custom emoji image if available, fall back to treating it as a Like.

3. Quote posts — Misskey sends _misskey_quote and quoteUrl on Note objects. Also check for fedibird:quoteUri (Fedibird/Mastodon compatibility). Display as an embedded quote if your platform supports it.

4. MFM content — notes from Misskey contain HTML in content (with MFM effects stripped) and optionally MFM source in the source property. Use the HTML for display; the MFM source is only useful if you want to re-render with a MFM parser (library: mfm-js).

5. isCat property on actors — a boolean extension. Misskey-family clients show cat ears and modify text display for cat-mode users. Safe to ignore but do not strip when forwarding actor documents.

6. Chat messages — notes with _misskey_talk: true are Misskey chat messages. They federate as normal Notes to non-Misskey platforms. Display as regular posts if your platform has no chat feature.

7. All API endpoints use POST — unlike Mastodon's REST conventions, Misskey uses POST for everything including reads. If implementing a Misskey-compatible API, every endpoint must accept POST.

8. Visibility level "home" — Misskey has a fourth visibility level (home) where notes are visible to everyone but excluded from the local and global timelines. This maps to ActivityPub to: followers, cc: Public (the inverse of Mastodon's "unlisted"). Handle carefully when federating.

9. Poll vote counts — Misskey includes _misskey_votes on poll options. This is equivalent to replies.totalItems but may be more reliably present. Prefer _misskey_votes when available.

10. Note content restrictions — the _misskey_makeNotesFollowersOnlyBefore and _misskey_makeNotesHiddenBefore properties on actors signal that historical content has access restrictions. Respect these when fetching older notes from Misskey actors.

---

10. Known Considerations

• No post editing in core Misskey — users must delete and redraft. The Sharkey fork adds federated note editing with version history.
• Cannot follow hashtags — use Antennas (keyword-filtered feeds) instead.
• No official mobile apps — third-party options include SocialHub (iOS) and Milktea (Android). The web client supports PWA.
• Antennas exclude personal posts from their results.
• Mute functionality gaps regarding mentions.
• No MRF equivalent for regex-based content filtering (unlike Pleroma/Akkoma).
• November 2025 announcement about potentially replacing ActivityPub with "Misskey's own low-overhead federation system" — details unclear, impact on interoperability unknown.
• Geographic registration restrictions on misskey.io — initially blocked Europeans (GDPR concerns), later restricted to Japanese users, Korea allowed since February 2026.
• Recent security fixes — CVE-2026-28431, CVE-2026-28432, CVE-2026-28433 patched in version 2026.3.1.