nips/51.md

NIP-51
======

Lists
-----

`draft` `optional` `author:fiatjaf` `author:arcbtc` `author:monlovesmango` `author:eskema` `author:gzuuus`

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`.

## Types of lists

### Generic lists

The kind `30001` has been reserved for generic lists. These must be accompanied by a `d` tag identifying the
list, but these have no standard meaning and are generally client-specific (except in the standard cases
specified below).

## Standard lists

Users are expected to have a single list of each of these types. They have special meaning and clients may
rely on them to augment the user 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)                 |
| Pin list         | 10001 | events the user intends to showcase in their profile page | `"e"` (kind:1 notes)                              |
| Bookmarks list   | 10003 | things the user intends to save for the future            | `"e"` (kind:1 notes), `"a"` (kind:30023 articles) |
| Communities list | 10004 | [NIP-72](72.md) communities the user belongs to           | `"a"` (kind:34550 community definitions)          |

## 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"` tag 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 variadic operations | `"relay"` (relay 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) |

## 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"
    ],
    [
      "title",
      "Yaks"
    ],
    [
      "summary",
      "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."
    ],
    [
      "image",
      "https://cdn.britannica.com/40/188540-050-9AC748DE/Yak-Himalayas-Nepal.jpg"
    ],
    ["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
```