Events

Events are the atomic unit of the Nostr protocol. This is a short overview of various types of events.

What is an Event?

Events are the only object type on the Nostr network. Here is one example:

{
  "id": "4376c65d2f232afbe9b882a35baa4f6fe8667c4e684749af565f981833ed6a65",
  "pubkey": "6e468422dfb74a5738702a8823b9b28168abab8655faacb6853cd0ee15deee93",
  "created_at": 1673347337,
  "kind": 1,
  "content": "Walled gardens became prisons, and nostr is the first step towards tearing down the prison walls.",
  "tags": [
    ["e", "3da979448d9ba263864c4d6f14984c423a3838364ec255f03c7904b1ae77f206"],
    ["p", "bf2376e17ba4ec269d10fcc996a4746b451152be9031fa48e74553dde5526bce"]
  ],
  "sig": "908a15e46fb4d8675bab026fc230a0e3542bfade63da02d542fb78b2a8513fcd0092619a2c8c1221e581946e0191f2af505dfdf8657a414dbca329186f009262"
}

The event above has kind 1, which means it is a "text note", i.e. a normal, simple, short, plaintext note, intended to be used in Twitter-like feeds, replies and comments.

Each kind number means something. For example, 0 is a "metadata" event, used for users to give details about themselves, such as their name and a profile picture. Relays can give different treatment to different kinds. For example, relays will generally delete older versions of kind:0 events and keep only the last one, while they will generally keep multiple 1 for each key.

You generally don't need more than kinds 0 and 1 to build a basic social-networking Nostr app, but other kinds were invented out of necessity by clients to provide other functionalities. They are specified in the NIPs. Some kinds are unrelated to social-networking and serve other needs from clients specific to these other functionalities. The idea is that, for each new use case one can think of in Nostr, a subprotocol must be thought about and proposed as a NIP, for maximum interoperability with existing and future clients that may be interested in implementing that functionality -- while also ensuring backwards-compatibility and nice fallbacks for everything that exists and does not want to change.

The created_at property is a UNIX timestamp set by the event creator, normally to the time it was created, but there are no checks made against that, but that is not a problem.

The content is dependent of what the kind means. In the case of kind:1, it is just a plaintext string meant to be read by others.

Similarly, tags also dependent on the kind, but some common tags that usually show up in kind:1 events but also in other kinds are "p", which is used to mention a public key, and "e", used to refer to another event.