Relays may provide server metadata to clients to inform them of capabilities, administrative contacts, and various server attributes. This is made available as a JSON document over HTTP, on the same URI as the relay's websocket.
When a relay receives an HTTP(s) request with an `Accept` header of `application/nostr+json` to a URI supporting WebSocket upgrades, they SHOULD return a document with the following structure.
Any field may be omitted, and clients MUST ignore any additional fields they do not understand. Relays MUST accept CORS requests by sending `Access-Control-Allow-Origin`, `Access-Control-Allow-Headers`, and `Access-Control-Allow-Methods` headers.
Field Descriptions
-----------------
### Name ###
A relay may select a `name` for use in client software. This is a string, and SHOULD be less than 30 characters to avoid client truncation.
### Description ###
Detailed plain-text information about the relay may be contained in the `description` string. It is recommended that this contain no markup, formatting or line breaks for word wrapping, and simply use double newline characters to separate paragraphs. There are no limitations on length.
### Pubkey ###
An administrative contact may be listed with a `pubkey`, in the same format as Nostr events (32-byte hex for a `secp256k1` public key). If a contact is listed, this provides clients with a recommended address to send encrypted direct messages (See `NIP-04`) to a system administrator. Expected uses of this address are to report abuse or illegal content, file bug reports, or request other technical assistance.
Relay operators have no obligation to respond to direct messages.
### Contact ###
An alternative contact may be listed under the `contact` field as well, with the same purpose as `pubkey`. Use of a Nostr public key and direct message SHOULD be preferred over this. Contents of this field SHOULD be a URI, using schemes such as `mailto` or `https` to provide users with a means of contact.
### Supported NIPs ###
As the Nostr protocol evolves, some functionality may only be available by relays that implement a specific `NIP`. This field is an array of the integer identifiers of `NIP`s that are implemented in the relay. Examples would include `1`, for `"NIP-01"` and `9`, for `"NIP-09"`. Client-side `NIPs` SHOULD NOT be advertised, and can be ignored by clients.
### Software ###
The relay server implementation MAY be provided in the `software` attribute. If present, this MUST be a URL to the project's homepage.
### Version ###
The relay MAY choose to publish its software version as a string attribute. The string format is defined by the relay implementation. It is recommended this be a version number or commit identifier.
Extra Fields
-----------------
### Server Limitations ###
These are limitations imposed by the relay on clients. Your client
should expect that requests which exceed these *practical* limitations
are rejected or fail immediately.
```json
{
...
"limitation": {
"max_message_length": 16384,
"max_subscriptions": 20,
"max_filters": 100,
"max_limit": 5000,
"max_subid_length": 100,
"min_prefix": 4,
"max_event_tags": 100,
"max_content_length": 8196,
"min_pow_difficulty": 30,
"auth_required": true,
"payment_required": true,
}
...
}
```
-`max_message_length`: this is the maximum number of bytes for incoming JSON that the relay
will attempt to decode and act upon. When you send large subscriptions, you will be
limited by this value. It also effectively limits the maximum size of any event. Value is
calculated from `[` to `]` and is after UTF-8 serialization (so some unicode characters
will cost 2-3 bytes). It is equal to the maximum size of the WebSocket message frame.
-`max_subscriptions`: total number of subscriptions that may be
active on a single websocket connection to this relay. It's possible
that authenticated clients with a (paid) relationship to the relay
may have higher limits.
-`max_filters`: maximum number of filter values in each subscription.
Must be one or higher.
-`max_subid_length`: maximum length of subscription id as a string.
-`min_prefix`: for `authors` and `ids` filters which are to match against
a hex prefix, you must provide at least this many hex digits in the prefix.
-`max_limit`: the relay server will clamp each filter's `limit` value to this number.
This means the client won't be able to get more than this number
of events from a single subscription filter. This clamping is typically done silently
by the relay, but with this number, you can know that there are additional results
if you narrowed your filter's time range or other parameters.
-`max_event_tags`: in any event, this is the maximum number of elements in the `tags` list.
-`max_content_length`: maximum number of characters in the `content`
field of any event. This is a count of unicode characters. After
serializing into JSON it may be larger (in bytes), and is still
subject to the `max_message_length`, if defined.
-`min_pow_difficulty`: new events will require at least this difficulty of PoW,
based on [NIP-13](13.md), or they will be rejected by this server.
-`auth_required`: this relay requires [NIP-42](42.md) authentication
to happen before a new connection may perform any other action.
Even if set to False, authentication may be required for specific actions.
-`payment_required`: this relay requires payment before a new connection may perform any action.
### Event Retention ###
There may be a cost associated with storing data forever, so relays
may wish to state retention times. The values stated here are defaults
for unauthenticated users and visitors. Paid users would likely have
other policies.
Retention times are given in seconds, with `null` indicating infinity.
If zero is provided, this means the event will not be stored at
all, and preferably an error will be provided when those are received.
