Reactions

A reaction is a kind 7 event that is used to indicate user reactions to other events. A reaction's content field MUST include user-generated-content indicating the value of the reaction (conventionally +, -, or an emoji).

A reaction with content set to + or an empty string MUST be interpreted as a "like" or "upvote". A reaction with content set to - MUST be interpreted as a "dislike" or "downvote".

A reaction with content set to an emoji or NIP-30 custom emoji SHOULD NOT be interpreted as a "like" or "dislike". Clients MAY instead display this emoji reaction on the post.

Tags

There MUST be always an e tag set to the id of the event that is being reacted to. The e tag SHOULD include a relay hint pointing to a relay where the event being reacted to can be found. If a client decides to include other e, which not recommended, the target event id should be last of the e tags.

There SHOULD be a p tag set to the pubkey of the event being reacted to. If a client decides to include other p tags, which not recommended, the target event pubkey should be last the p tags.

If the event being reacted to is an addressable event, an a SHOULD be included together with the e tag, it must be set to the coordinates (kind:pubkey:d-tag) of the event being reacted to.

The e and a tags SHOULD include relay and pubkey hints. The p tags SHOULD include relay hints.

The reaction event MAY include a k tag with the stringified kind number of the reacted event as its value.

Example code

func make_like_event(pubkey: String, privkey: String, liked: NostrEvent, hint: String) -> NostrEvent {
    var tags: [[String]] = []
    tags.append(["e", liked.id, hint, liked.pubkey])
    tags.append(["p", liked.pubkey, hint])
    tags.append(["k", String(liked.kind)])
    let ev = NostrEvent(content: "+", pubkey: pubkey, kind: 7, tags: tags)
    ev.calculate_id()
    ev.sign(privkey: privkey)
    return ev
}

External Content Reactions

If the target of a reaction is not a native nostr event, the reaction MUST be a kind 17 event and MUST include NIP-73 external content k + i tags to properly reference the content.

Reacting to a website:

{
  "kind": 17,
  "content": "⭐",
  "tags": [
    ["k", "web"],
    ["i", "https://example.com"]
  ],
}

Reacting to a podcast episode:

{
  "kind": 17,
  "content": "+",
  "tags": [
    ["k", "podcast:guid"],
    ["i", "podcast:guid:917393e3-1b1e-5cef-ace4-edaa54e1f810", "https://fountain.fm/show/QRT0l2EfrKXNGDlRrmjL"],
    ["k", "podcast:item:guid"],
    ["i", "podcast:item:guid:PC20-229", "https://fountain.fm/episode/DQqBg5sD3qFGMCZoSuLF"]
  ],
}

Custom Emoji Reaction

The client may specify a custom emoji (NIP-30) :shortcode: in the reaction content. The client should refer to the emoji tag and render the content as an emoji if shortcode is specified.

{
  "kind": 7,
  "content": ":soapbox:",
  "tags": [
    ["emoji", "soapbox", "https://gleasonator.com/emoji/Gleasonator/soapbox.png"]
  ],
  // other fields...
}

The content can be set only one :shortcode:. And emoji tag should be one.