nips/02.md
2023-04-17 13:31:18 -03:00

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# NIP-02
## Contact List and Petnames
`final` `optional` `author:fiatjaf` `author:arcbtc`
A special event with kind `3`, meaning "contact list" is defined as having a list of `p` tags, one for each of the followed/known profiles one is following.
Each tag entry should contain the key for the profile, a relay URL where events from that key can be found (can be set to an empty string if not needed), and a local name (or "petname") for that profile (can also be set to an empty string or not provided), i.e., `["p", <32-bytes hex key>, <main relay URL>, <petname>]`. The `content` can be anything and should be ignored.
For example:
```json
{
"kind": 3,
"tags": [
["p", "91cf9..4e5ca", "wss://alicerelay.com/", "alice"],
["p", "14aeb..8dad4", "wss://bobrelay.com/nostr", "bob"],
["p", "612ae..e610f", "ws://carolrelay.com/ws", "carol"]
],
"content": "",
...other fields
}
```
Every new contact list that gets published overwrites the past ones, so it should contain all entries. Relays and clients SHOULD delete past contact lists as soon as they receive a new one.
## Uses
### Contact list backup
If one believes a relay will store their events for sufficient time, they can use this kind-3 event to backup their following list and recover on a different device.
### Profile discovery and context augmentation
A client may rely on the kind-3 event to display a list of followed people by profiles one is browsing; make lists of suggestions on who to follow based on the contact lists of other people one might be following or browsing; or show the data in other contexts.
### Relay sharing
A client may publish a full list of contacts with good relays for each of their contacts so other clients may use these to update their internal relay lists if needed, increasing censorship-resistance.
### Petname scheme
The data from these contact lists can be used by clients to construct local ["petname"](http://www.skyhunter.com/marcs/petnames/IntroPetNames.html) tables derived from other people's contact lists. This alleviates the need for global human-readable names. For example:
A user has an internal contact list that says
```json
[
["p", "21df6d143fb96c2ec9d63726bf9edc71", "", "erin"]
]
```
And receives two contact lists, one from `21df6d143fb96c2ec9d63726bf9edc71` that says
```json
[
["p", "a8bb3d884d5d90b413d9891fe4c4e46d", "", "david"]
]
```
and another from `a8bb3d884d5d90b413d9891fe4c4e46d` that says
```json
[
["p", "f57f54057d2a7af0efecc8b0b66f5708", "", "frank"]
]
```
When the user sees `21df6d143fb96c2ec9d63726bf9edc71` the client can show _erin_ instead;
When the user sees `a8bb3d884d5d90b413d9891fe4c4e46d` the client can show _david.erin_ instead;
When the user sees `f57f54057d2a7af0efecc8b0b66f5708` the client can show _frank.david.erin_ instead.