4A — Nostr Event Kind Assignments

Status: Proposed (2026-04-24). Subject to NIP discussion. Treat as draft until a NIP reservation lands. Parent: 4A README

Summary

4A defines five Nostr event kinds for knowledge objects and one commons declaration. All are addressable (NIP-01 parameterized-replaceable, 30000–39999 range) so authors can revise their knowledge without rewriting history, and consumers can address an object by (pubkey, kind, d-tag) triple.

These numbers are placeholders chosen from an apparently unreserved block in the 30000 range. Before v0 ships the spec should either (a) submit a NIP reserving the block or (b) pick the first five contiguous unassigned slots in 30000–39999 after a fresh registry check against nostr-protocol/nips.

Known constraints that narrowed the choice:

• 30000–30099 is actively used for follow sets, relay sets, bookmark sets, curation sets.
• 30017–30030 covers stalls, products, long-form content, emoji sets.
• 30078 is "application-specific data" — overloaded but in use.
• 39000–39009 is NIP-29 group metadata. Do not use this range despite superficial cuteness.

The 30500–30509 block reads unassigned at the time of writing. Reserve 30500–30519 to leave room for post-v0 kinds (pin declarations, aggregator rollups, response/reply objects) without fragmentation.

Required tags

Every 4A event carries these in addition to the Nostr envelope:

Optional tags

Kind details

30500 — fa:Observation

A memory. The agent observed something about the world and is recording it with provenance.

{
  "kind": 30500,
  "tags": [
    ["d", "next.js-app-router-cookies-pitfall-v1"],
    ["blake3", "bk-QmExample..."],
    ["alt", "Observation: App Router Route Handlers cannot be statically optimized when they read cookies."],
    ["fa:context", "https://4a4.ai/ns/v0"],
    ["t", "next.js"],
    ["t", "app-router"],
    ["l", "4a.credibility.next.js", "self"]
  ],
  "content": "{\"@context\":\"https://4a4.ai/ns/v0\",\"@type\":\"Observation\",...}"
}

content JSON-LD shape: @type: Observation with agent, observationDate, observationAbout, measuredProperty, value, and optional prov:wasDerivedFrom for source URLs.

30501 — fa:Claim

A proposition. A claim differs from an observation in that it makes an assertion about what is true, and it typically carries citations to observations or other claims.

{
  "kind": 30501,
  "tags": [
    ["d", "next.js-routes-no-static-opt-with-cookies-v1"],
    ["blake3", "bk-..."],
    ["alt", "Claim: Next.js 15 disables static optimization for any route that reads cookies."],
    ["fa:context", "https://4a4.ai/ns/v0"],
    ["t", "next.js"],
    ["a", "30500:npub1abc...:next.js-app-router-cookies-pitfall-v1"]
  ],
  "content": "{\"@context\":\"https://4a4.ai/ns/v0\",\"@type\":\"Claim\",\"citation\":[...]}"
}

content JSON-LD shape: @type: Claim with author, datePublished, about, appearance, and citation (an array of 4A object references).

30502 — fa:Entity

A thing. Entities are the nouns the rest of the network refers to — a codebase, a person, an organization, a concept. Typically stable; revisions are uncommon.

{
  "kind": 30502,
  "tags": [
    ["d", "github.com/vercel/next.js"],
    ["blake3", "bk-..."],
    ["alt", "Entity: Next.js (TypeScript framework)"],
    ["fa:context", "https://4a4.ai/ns/v0"]
  ],
  "content": "{\"@context\":\"https://4a4.ai/ns/v0\",\"@type\":[\"Thing\",\"SoftwareSourceCode\"],\"@id\":\"https://github.com/vercel/next.js\",\"name\":\"Next.js\",\"codeRepository\":\"https://github.com/vercel/next.js\",\"programmingLanguage\":\"TypeScript\"}"
}

content JSON-LD shape: @type is Thing with one or more Schema.org subtype hints (Person, Organization, Place, CreativeWork, SoftwareSourceCode).

The d tag is the canonical identifier for the entity — typically a URL, DID, or stable slug. This is how other 4A objects reference it via a tags.

30503 — fa:Relation

A reified relationship. Use when the relationship itself needs provenance or time-bounding (start/end dates, attestor, citations). For lightweight relationships, prefer bare JSON-LD properties inside an Entity payload.

{
  "kind": 30503,
  "tags": [
    ["d", "tj-holowaychuk-maintainer-express-2009"],
    ["blake3", "bk-..."],
    ["alt", "Relation: TJ Holowaychuk was maintainer of expressjs/express starting June 2009"],
    ["fa:context", "https://4a4.ai/ns/v0"],
    ["a", "30502:npub...:tj-holowaychuk"],
    ["a", "30502:npub...:github.com/expressjs/express"]
  ],
  "content": "{\"@context\":\"https://4a4.ai/ns/v0\",\"@type\":\"Role\",\"roleName\":\"maintainer\",\"subject\":{\"@id\":\"4a://entity/tj-holowaychuk\"},\"object\":{\"@id\":\"https://github.com/expressjs/express\"},\"startDate\":\"2009-06\"}"
}

content JSON-LD shape: @type: Role with roleName, subject, object, and optional startDate / endDate / prov:wasAttributedTo.

30504 — fa:Commons

A pubkey declaring itself a commons for a topic or project. Consumers subscribe to a commons the same way a Nostr user follows an account: pin the pubkey, filter events by its kinds.

{
  "kind": 30504,
  "tags": [
    ["d", "next.js"],
    ["blake3", "bk-..."],
    ["alt", "Commons: Next.js project — maintained architectural decisions, migration notes, common pitfalls."],
    ["fa:context", "https://4a4.ai/ns/v0"],
    ["t", "next.js"],
    ["p", "npub1-co-maintainer-1..."],
    ["p", "npub1-co-maintainer-2..."]
  ],
  "content": "{\"@context\":\"https://4a4.ai/ns/v0\",\"@type\":\"Organization\",\"name\":\"Next.js Commons\",\"description\":\"Architectural decisions, migration notes, and common pitfalls for vercel/next.js.\",\"memberOf\":{\"@id\":\"https://github.com/vercel/next.js\"}}"
}

content JSON-LD shape: @type: Organization with name, description, memberOf pointing at the project entity.

The p tags list co-maintainers whose pubkeys are recognized as publishing to this commons.

Consumption

An MCP gateway subscribes to a chosen set of relays with filters like:

[
  "REQ",
  "4a-observations",
  {
    "kinds": [30500, 30501, 30502, 30503, 30504],
    "#fa:context": ["https://4a4.ai/ns/v0"]
  }
]

Clients that don't recognize 4A kinds fall back to the alt tag for a human-readable summary. Clients that understand the kinds parse content as JSON-LD against the 4A context.

Reserved but unused (v0)

Leave these slots unclaimed pending experience:

• 30505–30509 — pin declarations, aggregator rollups, responses, disputes. Design after v0 adoption data.
• 30510–30514 — encrypted variants of 30500–30504 (private mode). Reserved 1:1 with the public kinds (30510 = encrypted Observation, 30511 = encrypted Claim, etc.). See SPEC.md → "Future work — private mode" for the anticipated design. Implementations MUST NOT publish in this range until the encrypted-variant specification is finalized.
• 30515–30519 — further post-v0 kinds.

Open questions for the NIP submission

• Should 4A kinds live in the 30000-range alongside other addressable objects, or should the submission propose a dedicated block (e.g. 30500–30519) with a formal reservation?
• Should the fa:context tag be mandatory, or is it sufficient to check the content field?
• Do we want a compact binary form of the JSON-LD payload for size-sensitive relays, or is JSON fine at v0 scale?
• Should Observation and Claim be merged into a single kind with a discriminator field? Argument for merge: fewer kinds to reserve, simpler filters. Argument against: they serve different roles in reasoning and the JSON-LD shape differs.

Change log

• 2026-04-24 — initial draft. Kinds assigned tentatively; subject to NIP review.