NIP-51
======

Lists
-----

`draft` `optional`

This NIP defines lists of things that users can create. Lists can contain references to anything, and these references can be **public** or **private**.

Public items in a list are specified in the event `tags` array, while private items are specified in a JSON array that mimics the structure of the event `tags` array, but stringified and encrypted using the same scheme from [NIP-04](04.md) (the shared key is computed using the author's public and private key) and stored in the `.content`.

When new items are added to an existing list, clients SHOULD append them to the end of the list, so they are stored in chronological order.

## Types of lists

## Standard lists

Standard lists use non-parameterized replaceable events, meaning users may only have a single list of each kind. They have special meaning and clients may rely on them to augment a user's profile or browsing experience.

For example, _mute lists_ can contain the public keys of spammers and bad actors users don't want to see in their feeds or receive annoying notifications from.

| name           | kind  | description                                                 | expected tag items                                                                |
| ---            | ---   | ---                                                         | ---                                                                               |
| Mute list      | 10000 | things the user doesn't want to see in their feeds          | `"p"` (pubkeys), `"t"` (hashtags), `"word"` (lowercase string), `"e"` (threads)   |
| Pinned notes   | 10001 | events the user intends to showcase in their profile page   | `"e"` (kind:1 notes)                                                              |
| Bookmarks      | 10003 | uncategorized, "global" list of things a user wants to save | `"e"` (kind:1 notes), `"a"` (kind:30023 articles), `"t"` (hashtags), `"r" (URLs)` |
| Communities    | 10004 | [NIP-72](72.md) communities the user belongs to             | `"a"` (kind:34550 community definitions)                                          |
| Public chats   | 10005 | [NIP-28](28.md) chat channels the user is in                | `"e"` (kind:40 channel definitions)                                             |
| Blocked relays | 10006 | relays clients should never connect to                      | `"relay"` (relay URLs)                                                            |
| Search relays  | 10007 | relays clients should use when performing search queries    | `"relay"` (relay URLs)                                                            |
| Interests      | 10015 | topics a user may be interested in and pointers             | `"t"` (hashtags) and `"a" (kind:30015 interest set)`                              |
| Emojis         | 10030 | user preferred emojis and pointers to emoji sets            | `"emoji"` (see [NIP-30](30.md)) and `"a"` (kind:30030 emoji set)                  |

## Sets

Sets are lists with well-defined meaning that can enhance the functionality and the UI of clients that rely on them. Unlike standard lists, users are expected to have more than one set of each kind, therefore each of them must be assigned a different `"d"` identifier.

For example, _relay sets_ can be displayed in a dropdown UI to give users the option to switch to which relays they will publish an event or from which relays they will read the replies to an event; _curation sets_ can be used by apps to showcase curations made by others tagged to different topics.

Aside from their main identifier, the `"d"` tag, sets can optionally have a `"title"`, an `"image"` and a `"description"` tags that can be used to enhance their UI.

| name          | kind  | description                                                                                  | expected tag items                                                                |
| ---           | ---   | ---                                                                                          | ---                                                                               |
| Follow sets   | 30000 | categorized groups of users a client may choose to check out in different circumstances      | `"p"` (pubkeys)                                                                   |
| Relay sets    | 30002 | user-defined relay groups the user can easily pick and choose from during various operations | `"relay"` (relay URLs)                                                            |
| Bookmark sets | 30003 | user-defined bookmarks categories , for when bookmarks must be in labeled separate groups    | `"e"` (kind:1 notes), `"a"` (kind:30023 articles), `"t"` (hashtags), `"r" (URLs)` |
| Curation sets | 30004 | groups of articles picked by users as interesting and/or belonging to the same category      | `"a"` (kind:30023 articles), `"e"` (kind:1 notes)                                 |
| Curation sets | 30005 | groups of videos picked by users as interesting and/or belonging to the same category      | `"a"` (kind:34235 videos)                               |
| Interest sets | 30015 | interest topics represented by a bunch of "hashtags"                                         | `"t"` (hashtags)                                                                  |
| Emoji sets    | 30030 | categorized emoji groups                                                                     | `"emoji"` (see [NIP-30](30.md))                                                   |

## Deprecated standard lists

Some clients have used these lists in the past, but they should work on transitioning to the [standard formats](#standard-lists) above.

| kind  | "d" tag         | use instead                   |
| ---   | ---             | ---                           |
| 30000 | `"mute"`        | kind 10000 _mute list_        |
| 30001 | `"pin"`         | kind 10001 _pin list_         |
| 30001 | `"bookmark"`    | kind 10003 _bookmarks list_   |
| 30001 | `"communities"` | kind 10004 _communities list_ |

## Examples

### A _mute list_ with some public items and some encrypted items

```json
{
  "id": "a92a316b75e44cfdc19986c634049158d4206fcc0b7b9c7ccbcdabe28beebcd0",
  "pubkey": "854043ae8f1f97430ca8c1f1a090bdde6488bd5115c7a45307a2a212750ae4cb",
  "created_at": 1699597889,
  "kind": 10000,
  "tags": [
    ["p", "07caba282f76441955b695551c3c5c742e5b9202a3784780f8086fdcdc1da3a9"],
    ["p", "a55c15f5e41d5aebd236eca5e0142789c5385703f1a7485aa4b38d94fd18dcc4"]
  ],
  "content": "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?iv=S3rFeFr1gsYqmQA7bNnNTQ==",
  "sig": "1173822c53261f8cffe7efbf43ba4a97a9198b3e402c2a1df130f42a8985a2d0d3430f4de350db184141e45ca844ab4e5364ea80f11d720e36357e1853dba6ca"
}
```

### A _curation set_ of articles and notes about yaks

```
{
  "id": "567b41fc9060c758c4216fe5f8d3df7c57daad7ae757fa4606f0c39d4dd220ef",
  "pubkey": "d6dc95542e18b8b7aec2f14610f55c335abebec76f3db9e58c254661d0593a0c",
  "created_at": 1695327657,
  "kind": 30004,
  "tags": [
    ["d", "jvdy9i4"],
    ["name", "Yaks"],
    ["picture", "https://cdn.britannica.com/40/188540-050-9AC748DE/Yak-Himalayas-Nepal.jpg"],
    ["about", "The domestic yak, also known as the Tartary ox, grunting ox, or hairy cattle, is a species of long-haired domesticated cattle found throughout the Himalayan region of the Indian subcontinent, the Tibetan Plateau, Gilgit-Baltistan, Tajikistan and as far north as Mongolia and Siberia."],
    ["a", "30023:26dc95542e18b8b7aec2f14610f55c335abebec76f3db9e58c254661d0593a0c:95ODQzw3ajNoZ8SyMDOzQ"],
    ["a", "30023:54af95542e18b8b7aec2f14610f55c335abebec76f3db9e58c254661d0593a0c:1-MYP8dAhramH9J5gJWKx"],
    ["a", "30023:f8fe95542e18b8b7aec2f14610f55c335abebec76f3db9e58c254661d0593a0c:D2Tbd38bGrFvU0bIbvSMt"],
    ["e", "d78ba0d5dce22bfff9db0a9e996c9ef27e2c91051de0c4e1da340e0326b4941e"]
  ],
  "content": "",
  "sig": "a9a4e2192eede77e6c9d24ddfab95ba3ff7c03fbd07ad011fff245abea431fb4d3787c2d04aad001cb039cb8de91d83ce30e9a94f82ac3c5a2372aa1294a96bd"
}
```

## Encryption process pseudocode

```scala
val private_items = [
  ["p", "07caba282f76441955b695551c3c5c742e5b9202a3784780f8086fdcdc1da3a9"],
  ["a", "a55c15f5e41d5aebd236eca5e0142789c5385703f1a7485aa4b38d94fd18dcc4"],
]
val base64blob = nip04.encrypt(json.encode_to_string(private_items))
event.content = base64blob
```