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+# NIP-66: Relay Discovery and Liveness Monitoring
+
+`draft` `optional`
+
+You want to find relays. You may want to discover relays based on criteria that's up to date. You may even want to ensure that you have a complete dataset. You probably want to filter relays based on their reported liveness.
+
+In its purest form:
+
+```json
+{
+  "kind": 30166,
+  "created_at": 1722173222,  
+  "content": "{}",
+  "tags": [
+    [ "d", "wss://somerelay.abc/" ]
+  ],
+  "pubkey": "<pubkey>", 
+  "sig": "<signature>",
+  "id": "<eventid>"
+}
+```
+
+This event signals that the relay at `wss://somerelay.abc/` was reported "online" by `<pubkey>` at timestamp `1722173222`. This event **MAY** be extended upon to include more information.
+
+## Kinds
+`NIP-66` defines two (2) event kinds, `30166` and `10166`
+
+| kind  | name                       | description                                                                             |
+|-------|----------------------------|-----------------------------------------------------------------------------------------|
+| [30166](#k30166) | Relay Discovery      | A PRE that is published by a monitor when a relay is online |
+| [10166](#k10166) | Relay Monitor Announcement | An RE that stores data that signals the intent of a pubkey to monitor relays and publish `30166` events at a regular _frequency_ |
+
+## Ontology
+- `Relay Operator`: someone who operates a relay 
+- `Monitor`: A pubkey that monitors relays and publishes `30166` events at the frequency specified in their `10166` event.
+- `Ad-hoc Monitor`: A pubkey that monitors relays and publishes `30166` events at an irregular frequency.
+- `Monitor Service`: A group or individual that monitors relays using one or more `Monitors`.
+- `Check`: a specific data point that is tested or aggregated by a monitor.
+
+## `30166`: "Relay Discovery" <a id="k30166"></a>
+
+### Summary
+`30166` is a `NIP-33` Parameterized-Replaceable Event [PRE], referred to as a "Relay Discovery" event. These events are optimized with a small footprint for protocol-level relay Discovery.
+
+### Purpose 
+Discovery of relays over nostr. 
+
+### Schema 
+
+#### Content 
+`30166` content fields **SHOULD** include the stringified JSON of the relay's NIP-11 informational document. This data **MAY** be provided for informational purposes only. 
+
+#### `created_at`
+The `created_at` field in a NIP-66 event should reflect the time when the relay liveness (and potentially other data points) was checked.
+
+#### `tags`
+
+##### Meta Tags (unindexed)
+- `rtt-open` The relay's open **round-trip time** in milliseconds.
+- `rtt-read` The relay's read **round-trip time** in milliseconds.
+- `rtt-write` The relay's write **round-trip time** in milliseconds.
+
+_Other `rtt` values **MAY** be present. This NIP should be updated if there is value found in more `rtt` values._
+
+##### Single Letter Tags (indexed)
+- `d` The relay URL/URI. The `#d` tag **must** be included in the `event.tags[]` array. Index position `1` **must** be the relay websocket URL/URI. If a URL it **SHOULD** be [normalized](https://datatracker.ietf.org/doc/html/rfc3986#section-6). For relays not accessible via conventional means but rather by an npub/pubkey, an npub/pubkey **MAY** be used in place of a URL.
+  ```json
+  [ "d", "wss://somerelay.abc/"]
+  ```
+
+- `n`: Network
+  ```json
+  [ "n", "clearnet" ]
+  ```
+
+- `T`: Relay Type. Enumerated [relay type](https://github.com/nostr-protocol/nips/issues/1282) formatted as `PascalCase`
+  ```json
+  ["T", "PrivateInbox" ]
+  ```
+
+- `N`: Supported Nips _From NIP-11 "Informational Document" `nip11.supported_nips[]`_
+  ```json
+  [ "N", "42" ]
+  ```
+
+- `R`: Requirements _NIP-11 "Informational Document" `nip11.limitations.payment_required`, `nip11.limitations.auth_required` and/or any other boolean value within `nip11.limitations[]` that is added in the future_
+  ```json
+  [ "R", "payment" ],
+  [ "R", "auth" ],
+  ```
+  Since the nostr protocol does not currently support filtering on whether an indexed tag **is** or **is not** set, to make "public" and "no auth" relays discoverable requires a `!` flag
+
+  ```json
+  [ "R", "!payment" ], //no payment required, is public
+  [ "R", "!auth" ], //no authentication required
+  ```
+
+- `t`: "Topics" _From NIP-11 "Informational Document" `nip11.tags[]`_
+  ```json
+  [ "t", "nsfw" ]
+  ```
+
+- `k`: Accepted/Blocked Kinds [`NIP-22`]
+  ```json
+  [ "k", "0" ],
+  [ "k", "3" ],
+  [ "k", "10002" ]
+  ```
+
+  or for blocked kinds
+
+  ```json
+  [ "k", "!0" ]
+  [ "k", "!3" ],
+  [ "k", "!10002" ]
+  ```
+
+- `g`: `NIP-52` `g` tags (geohash)
+  ```json
+  [ "g", "9r1652whz" ]
+  ```
+
+- `30166` **MAY** be extended with global tags defined by other NIPs that do no collide with locally defined indices, including but not limited to: `p`, `t`, `e`, `a`, `i` and `l/L`. 
+
+#### Robust Example of a `30166` Event
+_Relay was online, and you can filter on a number of different tags_
+```json
+{
+  "id": "<eventid>",
+  "pubkey": "<monitor's pubkey>",
+  "created_at": "<created_at  [some recent date ...]>",
+  "signature": "<signature>",
+  "content": "{}",
+  "kind": 30166,
+  "tags": [  
+    ["d","wss://some.relay/"],
+    ["n", "clearnet"],
+    ["N", "40"],
+    ["N", "33"],
+    ["R", "!payment"],
+    ["R", "auth"],
+    ["g", "ww8p1r4t8"],
+    ["p", "somehexkey..."],
+    ["l", "en", "ISO-639-1"],
+    ["t", "nsfw" ],
+    ["rtt-open", 234 ]
+  ]
+} 
+```
+
+## `10166`: "Relay Monitor Announcement" Events <a id="k10166"></a>
+
+### Summary 
+`10166` is a replacable event herein referred to as "Relay Monitor Announcement" events. These events contain information about a publisher's intent to monitor and publish data as `30166` events. This event is optional and is intended for monitors who intend to provide monitoring services at a regular and predictable frequency.
+
+### Purpose 
+To provide a directory of monitors, their intent to publish, their criteria and parameters of monitoring activities. Absence of this event implies the monitor is ad-hoc and does not publish events at a predictable frequency, and relies on mechanisms to infer data integrity, such as web-of-trust.
+
+### Schema
+
+#### Standard Tags
+
+- `frequency` The frequency **in seconds** at which the monitor publishes events. A string-integer at index `1` represents the expected frequency the monitor will publish `30166` events. There should only be `1` frequency per monitor. 
+
+  ```json
+  [ "frequency", "3600" ]
+  ```
+
+- `timeout` (optional) The timeout values for various checks conducted by a monitor. Index `1` is the monitor's timeout in milliseconds. Index `2` describes what test the timeout is used for. If no index `2` is provided, it is inferred that the timeout provided applies to all tests. These values can assist relay operators in understanding data signaled by the monitor in _Relay Discovery Events_. 
+  ```json
+  [ "timeout", "2000", "open" ],
+  [ "timeout", "2000", "read" ],
+  [ "timeout", "3000", "write" ],
+  [ "timeout", "2000", "nip11" ],
+  [ "timeout", "4000", "ssl" ]
+  ```
+
+#### Indexed Tags
+- `c`  "Checks" **SHOULD** be a lowercase string describing the check(s) conducted by a monitor. Due to the rapidly evolving nature of relays, enumeration is organic and not strictly defined. But examples of some checks could be websocket `open/read/write/auth`, `nip11` checks, `dns` and `geo` checks, and and any other checks the monitor may deem useful.. Other checks **MAY** be included. New types of checks **SHOULD** be added to this NIP as they are needed.
+  ```json
+  [ "c", "ws" ],
+  [ "c", "nip11" ],
+  [ "c", "dns" ],
+  [ "c", "geo" ],
+  [ "c", "ssl" ],
+  ```
+
+- `g`: `NIP-52` `g` tags (geohash)
+  ```json
+  [ "g", "9r1652whz" ]
+  ```
+
+- Any other globally defined indexable tags **MAY** be included as found necessary.
+
+### Other Requirements
+Monitors **SHOULD** have the following 
+- A published `0` (NIP-1) event
+- A published `10002` (NIP-65) event that defines the relays the monitor publishes to.
+
+### Robust Example of a `10166` Event
+```json
+{
+  "id": "<eventid>",
+  "pubkey": "<monitor's pubkey>",
+  "created_at": "<created_at  [some recent date ...]>",
+  "signature": "<signature>",
+  "content": "",
+  "tags": [  
+
+    [ "timeout", "open", "5000"  ],
+    [ "timeout", "read", "3000"  ],
+    [ "timeout", "write", "3000" ],
+    [ "timeout", "nip11", "3000" ],
+
+    [ "frequency", "3600" ],
+
+    [ "c", "ws" ],
+    [ "c", "nip11" ],
+    [ "c", "ssl" ],
+    [ "c", "dns" ],
+    [ "c", "geo" ]
+
+    [ "g", "ww8p1r4t8" ]
+  ]
+} 
+```
+
+## Methodology 
+
+### Monitors
+1. A _Relay Monitor_ checks the liveness and potentially other attributes of a relay. 
+
+2. _Relay Monitor_ publishes a kind `30166` note when a relay it is monitoring is online. If the monitor has a `10166` event, events should be published at the frequency defined in their `10166` note. 
+
+_Any pubkey that publishes `30166` events **SHOULD** at a minimum be checking that the relay is available by websocket and behaves like a relay_
+
+### Clients
+1. In most cases, a client **SHOULD** filter on `30166` events using either a statically or dynamically defined monitor's `pubkey` and a `created_at` value respective of the monitor's published `frequency`. If the monitor has no stated frequency, other mechanisms should be employed to determine data integrity.
+
+2. _Relay Liveness_ is subjectively determined by the client, starting with the `frequency` value of a monitor. 
+
+3. The liveness of a _Relay Monitor_ can be subjectively determined by detecting whether the _Relay Monitor_ has published events with respect to `frequency` value of any particular monitor.
+
+4. The reliability and trustworthiness of a _Relay Monitor_ could be established via web-of-trust, reviews or similar mechanisms. 
+
+## Risk Mitigation
+
+- When a client implements `NIP-66` events, the client should have a fallback if `NIP-66` events cannot be located.
+
+- A `Monitor` or `Ad-hoc Monitor` may publish erroneous `30166` events, intentionally or otherwise. Therefor, it's important to program defensively to limit the impact of such events. This can be achieved with web-of-trust, reviews, fallbacks and/or data-aggregation for example.