NIP-51 defines list events for organizing users, events, relays, hashtags, and other references. It is the main protocol for bookmarks, mute lists, follow sets, relay sets, and several other user-curated collections.

Standard Lists and Sets

  • Standard lists use replaceable event kinds such as kind 10000 mute lists, kind 10003 bookmarks, and kind 10007 search relays.
  • Sets use addressable kinds with d tags, such as kind 30000 follow sets, kind 30003 bookmark sets, and kind 30030 emoji sets.

The distinction matters in client behavior. Standard lists imply one canonical list per user and kind. Sets imply many named collections, so clients must preserve each list’s d tag.

Structure

Lists use tags to reference content:

  • p tags for pubkeys
  • e tags for events
  • a tags for addressable events
  • t tags for hashtags
  • word tags for muted words
  • relay tags for relay URLs in relay-oriented list kinds

Some list kinds have narrower allowed tag shapes than others. For example, relay-oriented lists use relay tags, while bookmarks are expected to point to notes or addressable events. Clients that treat every NIP-51 list as arbitrary free-form tags will lose interoperability.

Public vs Private

Lists can have public tags and private items. Private items are serialized as a JSON array that mirrors the tags structure, encrypted, and stored in the event content. The current spec uses NIP-44 for this self-encryption model, with NIP-04 only as legacy compatibility.

That split lets users publish a visible list shell while hiding some entries. A bookmark list can stay public while private notes or private bookmarks remain in encrypted content.

Useful Kinds

  • Kind 10000: mute list for pubkeys, threads, hashtags, and muted words
  • Kind 10003: bookmarks for notes and addressable content
  • Kind 10007: preferred search relays
  • Kind 30002: relay sets for named relay groups
  • Kind 30006: picture curation sets
  • Kind 39089: starter packs for shareable follow bundles

Recent spec changes moved hashtags out of generic bookmarks and into interest sets, and added kind 30006 for picture curation. Both changes reduce ambiguity in how clients interpret list contents.

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