NIP-25
======

Reactions
---------

`draft` `optional`

A reaction is a `kind 7` event that is used to indicate user reactions to other events. A
reaction's `content` field MUST include a single character indicating the value of the reaction.
Reactions MUST NOT be used to support application-level semantics, they are for user-generated
content only.

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](30.md) custom emoji SHOULD NOT be interpreted
as a "like" or "dislike". Clients MAY instead display this emoji reaction on the post.

Tags
----

The reaction event SHOULD include `e` and `p` tags from the note the user is reacting to (and optionally `a` tags if the target is a replaceable event). This allows users to be notified of reactions to posts they were mentioned in. Including the `e` tags enables clients to pull all the reactions associated with individual posts or all the posts in a thread. `a` tags enables clients to seek reactions for all versions of a replaceable event.

The last `e` tag MUST be the `id` of the note that is being reacted to.

The last `p` tag MUST be the `pubkey` of the event being reacted to.

The `a` tag MUST contain the coordinates (`kind:pubkey:d-tag`) of the replaceable being reacted to.

The reaction event SHOULD include a `k` tag with the stringified kind number of the reacted event as
its value, and a `c` tag with the reaction's `content` so that reactions can be indexed and filtered.

Example code

```swift
func make_like_event(pubkey: String, privkey: String, liked: NostrEvent) -> NostrEvent {
    var tags: [[String]] = liked.tags.filter {
    	tag in tag.count >= 2 && (tag[0] == "e" || tag[0] == "p")
    }
    tags.append(["e", liked.id])
    tags.append(["p", liked.pubkey])
    tags.append(["k", liked.kind])
    let ev = NostrEvent(content: "+", pubkey: pubkey, kind: 7, tags: tags)
    ev.calculate_id()
    ev.sign(privkey: privkey)
    return ev
}
```

Reactions to a website
---------------------

If the target of the reaction is a website, the reaction MUST be a `kind 17` event and MUST include an `r` tag with the website's URL.

```jsonc
{
  "kind": 17,
  "content": "⭐",
  "tags": [
    ["r", "https://example.com/"]
  ],
  // other fields...
}
```

URLs SHOULD be [normalized](https://datatracker.ietf.org/doc/html/rfc3986#section-6), so that reactions to the same website are not omitted from queries.
A fragment MAY be attached to the URL, to react to a section of the page.
It should be noted that a URL with a fragment is not considered to be the same URL as the original.

Custom Emoji Reaction
---------------------

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

```jsonc
{
  "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.