Kind 41: Channel Metadata

Overview

Channel Metadata events (kind 41) are used to update information about an existing public chat channel in Nostr. Unlike creating a new channel (kind 40), these events modify properties of a channel without changing its identity, allowing channel owners to update details like name, description, picture, and recommended relay list.

Specification

Property	Value
Kind Number	41
Event Range	Regular
Defined in	NIP-28

Content Format

The content field contains a JSON string with the channel's updated metadata. This maintains the same structure as the metadata in kind 40 events, including properties like name, description, picture URL, and recommended relay list.

Schema

{
  "name": "Updated Channel Name",
  "about": "New channel description",
  "picture": "https://example.com/updated-image.jpg",
  "relays": [
    "wss://relay.example.com",
    "wss://another-relay.example.org"
  ]
}

Tags

Tag Name	Description	Format	Required
e	The channel creation event ID	["e", "<channel_event_id>", "<relay-url>", "root"]	Yes
t	Channel category/topic	["t", "technology"]	No
Other standard tags may be used as needed

Client Behavior

Clients should:

1. Only accept kind 41 events from the same pubkey that created the original channel (kind 40 event)
2. Update channel information when receiving a newer kind 41 event referencing a known channel
3. Consider only the most recent kind 41 event for each channel as valid
4. Display the updated channel information including name, description, and picture
5. Use the updated relay list to fetch and publish channel-related messages

Relay Behavior

Relays should:

1. Store these events like other regular events
2. Some relays may implement replaceable event functionality, keeping only the most recent kind 41 event per channel

Use Cases

• Updating channel names and descriptions
• Changing channel profile pictures
• Adding or removing recommended relays
• Adding or changing channel categories
• Keeping channel information current and accurate

Example

{
  "id": "5d83da77af1dec6d7289834998ad7aafbd9e2191396d75ec3cc27f5a77226f36",
  "pubkey": "79dff8f82963424e0bb02708a22e44b4980893e3a4be0fa3cb60a43b946764e3",
  "created_at": 1671217500,
  "kind": 41,
  "tags": [
    ["e", "4376c65d2f232afbe9b882a35baa4f6fe8667c4e684749af565f981833ed6a65", "wss://relay.example.com", "root"],
    ["t", "technology"],
    ["t", "programming"],
    ["t", "nostr"]
  ],
  "content": "{\"name\": \"Nostr Development & Research\", \"about\": \"An updated channel for discussing Nostr protocol development, research, and implementation\", \"picture\": \"https://example.com/nostr-dev-updated.png\", \"relays\": [\"wss://relay.example.com\", \"wss://nostr.example.org\", \"wss://new-relay.example.net\"]}",
  "sig": "a76f39224cebd44cf04eeebe01d5ab2e8f7a3e5e56c83cadd252e7bc5e2e34fd7ad7148cf7a2c7620d9490ccf2e1bac521995725f2e1f543159b8eb98bfdd405"
}

Channel Metadata Properties

The JSON in the content field typically includes:

• name (required): The updated name of the channel
• about (recommended): Updated channel description
• picture (optional): New URL to an image representing the channel
• relays (recommended): Updated array of relay URLs where channel messages should be published/fetched

Additional custom fields may be included for extended functionality.

Update Authority

Only the original creator of a channel (the pubkey that created the kind 40 event) has the authority to issue valid kind 41 updates. Clients should:

1. Verify that any kind 41 event comes from the same pubkey as the referenced channel's kind 40 event
2. Ignore kind 41 events from other pubkeys
3. Only apply the most recent valid update (based on the created_at timestamp)

References

• NIP-28: Public Chat
• NIP-10: Event References - For proper event referencing

Related Kinds

• Kind 40: Channel Creation - Create public chat channels
• Kind 42: Channel Message - Post messages in channels
• Kind 43: Channel Hide Message - Moderation tool to hide messages
• Kind 44: Channel Mute User - Moderation tool to mute users

Notes

• While kind 41 events allow for channel metadata updates, the fundamental identity of the channel (its event ID) remains the original kind 40 event
• Clients are responsible for validating the authenticity of metadata updates
• Multiple updates can be issued over time; only the most recent should be considered valid
• The e tag with the root marker is crucial for properly linking the metadata update to the original channel