Kind 42: Channel Message

Overview

Channel Message events (kind 42) are used to send text messages to public chat channels in Nostr. These events form the core content of the channel system, allowing users to communicate in shared spaces and engage in threaded conversations through replies.

Specification

Property	Value
Kind Number	42
Event Range	Regular
Defined in	NIP-28

Content Format

The content field contains the actual text message being sent to the channel. It can include plain text, markdown formatting, NIP-19 entities, and other conventional formatting used in Nostr content.

Schema

"content": "Hello channel! This is my first message here."

Tags

Tag Name	Description	Format	Required
e	Channel reference (root)	["e", "<channel_event_id>", "<relay-url>", "root"]	Yes
e	Referenced message (for replies)	["e", "<message_event_id>", "<relay-url>", "reply"]	For replies
p	Author of referenced message	["p", "<pubkey>", "<relay-url>"]	For replies
Other standard tags may be used as needed

Client Behavior

Clients should:

1. Display messages in chronological order within their respective channels
2. Support threaded conversations with proper reply formatting
3. When creating a new message:
   • Always include an e tag with the root marker referencing the channel's kind 40 event
   • For replies, include an additional e tag with the reply marker referencing the message being replied to
   • For replies, include a p tag referencing the author of the message being replied to
4. Post messages to the relays specified in the channel's metadata
5. Support message formatting, links, and other content features

Relay Behavior

Relays should:

1. Store these events like other regular events
2. Allow efficient querying of messages by channel ID

Use Cases

• Regular channel conversation
• Topic-based discussions
• Team communications
• Community interactions
• Questions and answers
• Threaded replies to specific messages

Example

Root Message (a new message in a channel):

{
  "id": "5d83da77af1dec6d7289834998ad7aafbd9e2191396d75ec3cc27f5a77226f36",
  "pubkey": "79dff8f82963424e0bb02708a22e44b4980893e3a4be0fa3cb60a43b946764e3",
  "created_at": 1671217500,
  "kind": 42,
  "tags": [
    ["e", "4376c65d2f232afbe9b882a35baa4f6fe8667c4e684749af565f981833ed6a65", "wss://relay.example.com", "root"]
  ],
  "content": "Has anyone managed to implement NIP-28 channels in their client yet? I'm looking for some examples.",
  "sig": "a76f39224cebd44cf04eeebe01d5ab2e8f7a3e5e56c83cadd252e7bc5e2e34fd7ad7148cf7a2c7620d9490ccf2e1bac521995725f2e1f543159b8eb98bfdd405"
}

Reply Message (responding to another message):

{
  "id": "6e3a6e22a68e6393943734af26db1de5894b5c21cff6a5b390f34fee83c0b77a",
  "pubkey": "f7234bd4c1394dda46d09f35bd384dd30cc552ad5541990f98844fb06676e9ca",
  "created_at": 1671217600,
  "kind": 42,
  "tags": [
    ["e", "4376c65d2f232afbe9b882a35baa4f6fe8667c4e684749af565f981833ed6a65", "wss://relay.example.com", "root"],
    ["e", "5d83da77af1dec6d7289834998ad7aafbd9e2191396d75ec3cc27f5a77226f36", "wss://relay.example.com", "reply"],
    ["p", "79dff8f82963424e0bb02708a22e44b4980893e3a4be0fa3cb60a43b946764e3", "wss://relay.example.com"]
  ],
  "content": "Yes, I've implemented it in my client. I can share some code examples if you'd like.",
  "sig": "b35c089ebad28490918dac8a033233258af89b132570b8f5191d95ebcb5c5cd7a0e9cf274b0ece0fc9d2c661237e9649a4cc4c28da86135c915788d35288b9c9"
}

Threading Model

NIP-28 uses a two-level threading model:

1. Root level: All messages in a channel reference the channel's kind 40 event with the root marker
2. Reply level: Replies reference both the channel (root) and the specific message they're responding to (reply)

This enables efficient retrieval of all messages in a channel while also maintaining threaded conversations.

References

• NIP-28: Public Chat
• NIP-10: Event References - For reply threading

Related Kinds

• Kind 40: Channel Creation - Create the channel
• Kind 41: Channel Metadata - Update channel information
• Kind 43: Channel Hide Message - Moderation feature
• Kind 44: Channel Mute User - Moderation feature

Notes

• The channel system is designed to be both simple and flexible
• All messages must reference the original kind 40 channel creation event
• Moderation is client-side; any user can post to any public channel
• Threading is implemented using the NIP-10 event referencing conventions
• For best user experience, clients should post messages to all relays listed in the channel metadata