Kind 4550: Community Post Approval

Overview

Community Post Approval events (kind 4550) are used by moderators to approve posts for inclusion in moderated communities. These events represent the moderation layer of the NIP-72 community system, allowing designated moderators to curate what content appears within a community. Any post in a Nostr community requires approval through a kind 4550 event before it can be considered part of that community.

Specification

Property	Value
Kind Number	4550
Event Range	Regular
Defined in	NIP-72

Content Format

The content field must contain the full JSON-encoded event being approved. This ensures that even if the original post is modified or deleted, the approved version remains available.

Schema

"content": "<JSON-encoded original post event>"

Tags

Tag Name	Description	Format	Required
a	Community reference	["a", "34550:<pubkey>:<d-identifier>", "<relay-url>"]	Yes
e	Post event reference	["e", "<event-id>", "<relay-url>"]	Yes*
a	Replaceable post reference	["a", "<type>:<pubkey>:<d-identifier>", "<relay-url>"]	Yes*
p	Post author reference	["p", "<pubkey>", "<relay-url>"]	Yes
k	Post event kind	["k", "<kind-number>"]	Yes

*Either an e tag or an a tag (or both) must be used to reference the post being approved, depending on the approval strategy.

Client Behavior

Clients should:

1. Only display posts in a community that have valid approval events from the community's moderators
2. When showing a moderated community:
   • Fetch community definition (kind 34550) to identify moderators
   • Fetch post approval events (kind 4550) from those moderators
   • Display only approved posts in the community view
   • Use the post kind from the k tag to allow filtering by event type
3. For clients used by moderators:
   • Provide an interface for reviewing and approving community posts
   • Generate proper kind 4550 events with all required tags
   • Include the full JSON-encoded original post in the content
4. Handle deletion requests (kind 5) targeting approval events as revocation of approval
5. For replaceable events, implement the three approval strategies:
   • When using e tag only: Approval applies to only that specific version
   • When using a tag only: Approval applies to all versions by that author
   • When using both: Display version history with appropriate UI

Relay Behavior

Relays should:

1. Store post approval events alongside the posts themselves
2. Honor deletion requests for approval events
3. Make approval events discoverable through standard filters

Use Cases

• Moderating content in topic-based communities
• Approving posts for inclusion in curated spaces
• Creating spam-free discussion environments
• Implementing community standards and guidelines
• Enabling content curation by trusted moderators
• Building Reddit-style community structures
• Supporting multi-moderator approval workflows

Example

{
  "id": "c8c87a8fd7c5c427fb2a6cf365d95e0f1c6ebefcf993118ce539e57f8e971c75",
  "pubkey": "3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d",
  "created_at": 1684324000,
  "kind": 4550,
  "tags": [
    ["a", "34550:32e1827635450ebb3c5a7d12c1f8e7b2b514439ac10a67eef3d9fd9c5c68e245:nostr-dev", "wss://relay.nostr.band"],
    ["e", "df0be4d4505c044c1063059e76db26cac90cf59a0be1e4e01fbef72012eac9e6", "wss://relay.nostr.band"],
    ["p", "854043ae8f1f97430ca8c1f1a090bdde6488bd5115c7a45307a2a212750ae4cb", "wss://relay.nostr.band"],
    ["k", "1"]
  ],
  "content": "{\"id\":\"df0be4d4505c044c1063059e76db26cac90cf59a0be1e4e01fbef72012eac9e6\",\"pubkey\":\"854043ae8f1f97430ca8c1f1a090bdde6488bd5115c7a45307a2a212750ae4cb\",\"created_at\":1684323950,\"kind\":1,\"tags\":[[\"a\",\"34550:32e1827635450ebb3c5a7d12c1f8e7b2b514439ac10a67eef3d9fd9c5c68e245:nostr-dev\",\"wss://relay.nostr.band\"]],\"content\":\"Has anyone implemented NIP-72 communities in their client yet?\",\"sig\":\"a9a4e2192eede77e6c9d24ddfab95ba3ff7c03fbd07ad011fff245abea431fb4d3787c2d04aad001cb039cb8de91d83ce30e9a94f82ac3c5a2372aa1294a96bd\"}",
  "sig": "915b6f8c1033a1a4f0c4b0f9bb46f3b1c071725f7c204bc1b3aa948b3098d0edd3487a9b387592ce3c9f095c4d30ccc0ed5d8be46f39933c46065a1742e3ec91"
}

Approval Strategies for Replaceable Events

NIP-72 defines three strategies for approving replaceable events:

1. Version-Specific Approval (e tag only):

   • Approves only the specific version of the event
   • Requires new approvals for any updates to the event
   • Useful for strict moderation where all changes need review

2. Author-Wide Approval (a tag only):

   • Approves all versions of the replaceable event by that author
   • Author can update without requiring new approvals
   • Good for trusted authors who may need to update content

3. Full History Approval (both e and a tags):

   • Provides approval for current and future versions
   • Preserves the specific version being approved
   • Enables clients to show history with appropriate UI indicators

References

• NIP-72: Moderated Communities
• NIP-09: Event Deletion
• NIP-18: Reposts

Related Kinds

• Kind 34550: Community Definition - Defines the community and its moderators
• Kind 10004: Communities - List of communities a user belongs to
• Kind 5: Event Deletion - Used to revoke approval for a post

Notes

• It's recommended that multiple moderators approve posts to develop resilience
• If a moderator is removed, their approval events may still be valid depending on client implementation
• When moderator rotation happens, new moderators may need to re-approve existing posts
• Clients may implement different policies on how many moderator approvals are needed
• The community owner can periodically re-sign approvals to ensure continuity
• For cross-posting, events can be approved in multiple communities with separate approval events
• In case of replaceable event approval, the content must contain the specific approved version if using e tag
• Clients should evaluate non-34550:* a tags as posts to be approved for all 34550:* a tags