Tags

Tags ^rat contain data that is indexed and searchable. All tags are searchable on servers. If an application requires unsearchable tags, these can be defined within that application's payload.

Tags are laid out as follows:

0       2        4         65536 max
+-------+--------+----------+
| len   | type   | value ...|
+-------+--------+----------+

• [0:2] - The length of the tag value as a little-endian unsigned integer. This length includes the len and type bytes and thus MUST be at least 4.
• [2:4] - The type of the tag. All tag types are listed in the Tag types registry.
• [4:] - The value, which is at most 65,532 bytes long.

Tag values are generally considered opaque at this layer, except for Core tags with the Core Application.

Unlike nostr, tags do not have multiple value fields. Applications can encode multiple fields into the 65,532 data bytes however they wish.

Applications SHOULD expect tags to be indexed by their type and some prefix of their value (of unspecified length, but it SHOULD include at least 22 bytes including the type). As a consequence, tags should be defined to front-load their unique aspects within the first 20 bytes of their value to maximize the effectiveness of indexes.