NIP-50
======

Keywords Filter
---------------

`draft` `optional` `author:brugeman` `author:mikedilger`

## Abstract

Many Nostr use cases require some form of search by `content` field. The meaning and format of `content` differs 
with event kind and use case. Thus, this NIP only establishes a general framework for search over `content`,
and specifies the details for kind `0` and kind `1` events.

## `keywords` filter field 

A new `keywords` field is introduced for `REQ` messages from clients:
```json
{
  "kinds": <an array of kind numbers>
  "keywords": <an array of strings>
}
```
A filter with `keywords` field MUST also include `kinds` field. This NIP specifies the behavior for kinds `0` and `1`, 
if none of these kinds are provided along with `keywords`, relay SHOULD ignore the filter, and MAY send
a `NOTICE` to inform the client. Future NIPs will specify behavior for other event kinds.

A filter matches if one of the provided `keywords` matches. Each keyword string may contain several conditions - `words`, 
all the words must match for a keyword to match. The meaning of `words` depends on event kind.

Clients SHOULD use the supported_nips field to learn if a relay supports keyword filter queries. Clients MAY send keyword filter queries to any relay, if they are prepared to filter out extraneous responses from relays that do not support this NIP.

Clients SHOULD query several relays supporting this NIP and specific kind to compensate for potentially different 
implementation details between relays (like string sanitization, etc).

Clients SHOULD verify that events returned by a relay match the specified `keywords` in the way that suits the
client's use case, and MAY stop querying relays that have low precision.

## Keyword search for kind `0` and kind `1` 

For kind `0` and kind `1`, each keyword is a lowercase string consisting of words separated by spaces (in most languages), punctuation/control 
characters are ignored. 

For kind `1`, an event must include all words in it's `content` field for it to match the keyword.

For kind `0`, an event must include all mentioned words in the json object stored at the `content` field. Recommended 
json fields for matching are `about`, `display_name`, `name`, `nip05`, `lud06` and `lud18`.

A keyword may contain a word starting with prefix `option:` (like `option:no_spam`), such words specify additional 
constraints for event matching, and are reserved for the future extensions. Relay SHOULD ignore `option:` words that it does not support.

Relay MAY support these options for kind `0` and kind `1` events:
- `option:no_spam` - only include events deemed 'high-quality' by whatever internal metric the relay adopts