Reactions

1 Overview

A reaction is a small event that points at another event and carries a short verdict. The verdict is a +, a -, or an emoji. Clients use reactions to build like buttons, upvote counters, and emoji rows.

This NIP defines two event kinds. Kind 7 reacts to a native Nostr event. Kind 17 reacts to external content, such as a website or a podcast episode. Both kinds are ordinary signed events from NIP-01. Any relay can store them. Any client can count them.

A reaction does not modify its target. It only references the target with tags. To count likes for a note, a client subscribes to kind 7 events whose e tag matches the note's id.

2 The Reaction Event (Kind 7)

A reaction is a kind 7 event. The content field must hold user-generated content that states the value of the reaction. The convention is +, -, or an emoji.

3 Tags

A kind 7 reaction locates its target with tags. The tag names come from NIP-01. Their rules here are:

Hints help clients find the target. The e and a tags should include relay and pubkey hints. The p tags should include relay hints.

The source NIP ships this reference routine. It builds a like for one target event with the recommended tags and hints:

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
}

4 External Content Reactions (Kind 17)

Sometimes the target is not a Nostr event. It is a web page, a podcast, or another external resource. In that case the reaction must be a kind 17 event. It must include NIP-73 external content k and i tags that reference the content. The k tag names the content type. The i tag holds the identifier, with an optional URL hint.

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

A target can carry more than one identifier pair. This reaction likes one episode of one podcast. Each i tag adds a URL hint as its third element:

{
  "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"]
  ]
}

5 Custom Emoji Reactions

A client may put a NIP-30 custom emoji :shortcode: in the reaction content. A matching emoji tag maps the shortcode to an image URL. When a shortcode is present, the client should read the emoji tag and render the content as that emoji.

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

Two limits apply. The content can hold only one :shortcode:. The event should carry only one emoji tag.

6 Worked Example

Alice publishes a kind 1 note. Bob likes it. The full reaction event and the relay session look like this:

{
  "id":         "9d3b1c44f0…",
  "pubkey":     "8c4f2ab9d1…",  // Bob
  "created_at": 1756713600,
  "kind":       7,
  "tags": [
    ["e", "b1a649ebe8…", "wss://relay.example.com", "22a12a12…"],
    ["p", "22a12a12…", "wss://relay.example.com"],
    ["k", "1"]
  ],
  "content":    "+",
  "sig":        "7f0ac2e91b…"
}

-- Bob publishes the reaction --
→ ["EVENT", {"id":"9d3b1c44f0…","kind":7,"content":"+",
     "tags":[["e","b1a649ebe8…","wss://relay.example.com","22a12a12…"],
             ["p","22a12a12…","wss://relay.example.com"],["k","1"]], …}]
← ["OK", "9d3b1c44f0…", true, ""]

-- Alice's client counts reactions to her note --
→ ["REQ", "reacts", {"kinds":[7], "#e":["b1a649ebe8…"]}]
← ["EVENT", "reacts", {"id":"9d3b1c44f0…", "kind":7, "content":"+", …}]
← ["EOSE", "reacts"]
-- content "+" or "" → like. "-" → dislike. emoji → shown as-is --
→ ["CLOSE", "reacts"]

7 Version History

NIP-25 started as a likes-and-dislikes spec for text notes. It grew to cover any event, custom emoji, and external content. Notable changes, newest first:

• 20252025-08Added external content reactions: kind 17 with NIP-73 k and i tags.
• 20252025-05Removed the rule that mapped emoji reactions to like or dislike. Added relay and pubkey hint recommendations.
• 20252025-02Discouraged extra e and p tags; the target must be the last tag of its letter.
• 20242024-05Added the a tag for addressable targets and the k kind tag. A broader "Simplifying reactions" rewrite was reverted in June.
• 20232023-08An empty content string now counts as +.
• 20232023-07Added custom emoji reactions with NIP-30 shortcodes.
• 20232023-01Allowed emojis to count as likes or dislikes (removed again in 2025).
• 20222022-08Reactions can target any event, not only text notes. The generic like became an explicit +.
• Origin2022-07William Casarin created NIP-25 with likes, dislikes, and downvotes (2022-07-30).

8 See Also

• NIP-01 — the base event format and the e, p, a tags reused here.
• NIP-30 — custom emoji: the :shortcode: and emoji tag format.
• NIP-73 — external content IDs: the k and i tags required by kind 17.
• NIP-10 — text notes and threads, the most common reaction targets.
• NIP-18 — reposts, the other lightweight response to a note.