constellation · intersection

<atproto-mutuals>

Intersection of two actor sets via Constellation's many-to-many endpoint. Default: who follows BOTH a and b. Override `source` for like/repost/reply/quote intersections.

Live

<!-- followers in common -->
<atproto-mutuals a="did:plc:..." b="did:plc:..." source="follow"></atproto-mutuals>

<!-- accounts that liked both posts -->
<atproto-mutuals a="at://.../post/x" b="at://.../post/y" source="like"></atproto-mutuals>

Attributes

Name	Type	Default	Description
`a` *	`string`	—	First subject (handle, DID, or AT-URI).
`b` *	`string`	—	Second subject — same shape as a.
`source`	`string`	`follow`	Relation key from SOURCES — follow, like, repost, reply, quote.
`limit`	`number`	`16`	Avatars per page.
`constellation`	`string`	—	Override the Constellation endpoint.

Parts

External CSS can target these via atproto-mutuals::part(<name>) { ... }.

Part	What it is
`head / grid / actor / actor-avatar / loadmore / empty`	Same as atproto-followers (shared actor-grid base).

What it does

Queries Constellation's getManyToMany XRPC endpoint with two subjects and a shared source:pathToOther. Returns DIDs whose records link to BOTH subjects via the named relation.

Out of the box the source defaults to follow — answering "who follows both of these people?" — but any key in the library's SOURCES table works: like, repost, reply, quote, follow.

Handle resolution gotcha

The a and b attributes accept handle, DID, or AT-URI. Handle resolution requires the handle's domain to serve /.well-known/atproto-did with CORS open. Most *.bsky.social handles don't, and custom domains vary — if either subject 404s on well-known resolution, the whole query fails with "Failed to fetch".

For reliable demos and production, pass DIDs directly. The demo above uses DIDs for both subjects to sidestep the issue entirely.

Use cases

Audience overlap: who follows both you and a peer? Useful for collaboration / audience analysis.
Content overlap: which accounts liked both a post and a related post? Proxy for topic resonance.
Conversation overlap: who replied to both threads?