chorus
ATProto-native community notes with bridging-based consensus
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Chorus #

ATProto-native community notes with bridging-based consensus.

Live: https://chorus.filae.site

What is this? #

Chorus implements Community Notes-style collaborative fact-checking for the AT Protocol. The key innovation: notes only get certified when they receive positive ratings from users with diverse perspectives.

A note isn't "helpful" because many people say so — it's helpful when people who usually disagree can agree it's helpful.

How it works #

The Algorithm #

Uses matrix factorization (Alternating Least Squares) to learn:

  • Note intercept (i_n): How helpful the note is, independent of perspective
  • Note factor (f_n): Which "side" the note appeals to
  • User intercept (i_u): User's general rating bias
  • User factor (f_u): User's perspective/ideology

A note is certified when:

  • i_n > 0.35 (genuinely helpful across perspectives)
  • |f_n| < 0.5 (not too aligned with any single perspective)
  • rating_count >= 5 (enough data to be confident)

Architecture #

User PDSes (ATProto)          Chorus (Cloudflare)
┌─────────────────────┐       ┌─────────────────────┐
│ site.filae.chorus   │       │ Worker              │
│   .note records     │──────▶│   - Index API       │
│   .rating records   │       │   - Query API       │
└─────────────────────┘       │   - Algorithm (cron)│
                              │                     │
                              │ D1 Database         │
                              │   - Aggregation     │
                              │   - Scores          │
                              └─────────────────────┘

Notes and ratings live in user PDSes (portable, user-owned). Chorus aggregates them and runs the bridging algorithm.

API #

Index endpoints #

# Index a note
curl -X POST https://chorus.filae.site/api/index/note \
  -H "Content-Type: application/json" \
  -d '{"uri": "at://did:plc:xxx/site.filae.chorus.note/yyy"}'

# Index a rating
curl -X POST https://chorus.filae.site/api/index/rating \
  -H "Content-Type: application/json" \
  -d '{"uri": "at://did:plc:xxx/site.filae.chorus.rating/yyy"}'

Query endpoints #

# Get notes for any AT-URI
curl "https://chorus.filae.site/api/notes?subject=at://..."

# Get only certified notes
curl "https://chorus.filae.site/api/certified?subject=at://..."

# Get a specific note with its ratings
curl "https://chorus.filae.site/api/note/did:plc:xxx/rkey"

# System stats
curl "https://chorus.filae.site/api/stats"

Lexicons #

site.filae.chorus.note #

A community note on any AT-URI:

{
  "subject": "at://did:plc:xxx/app.bsky.feed.post/yyy",
  "body": "The note content",
  "sources": ["https://example.com/source"],
  "createdAt": "2026-02-23T00:00:00Z"
}

site.filae.chorus.rating #

A rating on a note:

{
  "note": "at://did:plc:xxx/site.filae.chorus.note/yyy",
  "helpful": "yes",  // "yes" | "somewhat" | "no"
  "tags": ["clear", "sourced"],
  "createdAt": "2026-02-23T00:00:00Z"
}

Browser Extension #

The extension/ directory contains a Chrome extension that overlays community notes on Bluesky posts:

  1. Open chrome://extensions/
  2. Enable "Developer mode"
  3. Click "Load unpacked" and select the extension/ directory

As you browse Bluesky, posts with community notes will show a badge. Click to expand and see full note details.

Development #

bun install
bun run dev       # Local development
bun run test      # Run tests
bun run deploy    # Deploy to Cloudflare

References #