diff --git a/packages/nostr/src/client/conn.ts b/packages/nostr/src/client/conn.ts
index 3019710..8b24b0b 100644
--- a/packages/nostr/src/client/conn.ts
+++ b/packages/nostr/src/client/conn.ts
@@ -1,6 +1,6 @@
 import { ProtocolError } from "../error"
 import { Filters, SubscriptionId } from "."
-import { RawEvent, SignedEvent } from "../event"
+import { EventId, RawEvent, SignedEvent } from "../event"
 import WebSocket from "ws"
 import { unixTimestamp } from "../util"
 
@@ -14,7 +14,6 @@ import { unixTimestamp } from "../util"
  */
 export class Conn {
   readonly #socket: WebSocket
-
   /**
    * Messages which were requested to be sent before the websocket was ready.
    * Once the websocket becomes ready, these messages will be sent and cleared.
@@ -23,16 +22,26 @@ export class Conn {
   // before NIP-44 auth. The legacy code reuses the same array for these two but I think they should be
   // different, and the NIP-44 stuff should be handled by Nostr.
   #pending: OutgoingMessage[] = []
-
-  #msgCallback?: IncomingMessageCallback
-  #errorCallback?: ErrorCallback
+  /**
+   * Callback for errors.
+   */
+  readonly #onError: (err: unknown) => void
 
   get url(): string {
     return this.#socket.url
   }
 
-  constructor(endpoint: string | URL) {
-    this.#socket = new WebSocket(endpoint)
+  constructor({
+    url,
+    onMessage,
+    onError,
+  }: {
+    url: URL
+    onMessage: (msg: IncomingMessage) => void
+    onError: (err: unknown) => void
+  }) {
+    this.#onError = onError
+    this.#socket = new WebSocket(url)
 
     // Handle incoming messages.
     this.#socket.addEventListener("message", async (msgData) => {
@@ -40,14 +49,14 @@ export class Conn {
       // Validate and parse the message.
       if (typeof value !== "string") {
         const err = new ProtocolError(`invalid message data: ${value}`)
-        this.#errorCallback?.(err)
+        onError(err)
         return
       }
       try {
-        const msg = await parseIncomingMessage(value)
-        this.#msgCallback?.(msg)
+        const msg = await Conn.#parseIncomingMessage(value)
+        onMessage(msg)
       } catch (err) {
-        this.#errorCallback?.(err)
+        onError(err)
       }
     })
 
@@ -60,22 +69,10 @@ export class Conn {
     })
 
     this.#socket.addEventListener("error", (err) => {
-      this.#errorCallback?.(err)
+      onError(err)
     })
   }
 
-  on(on: "message", cb: IncomingMessageCallback): void
-  on(on: "error", cb: ErrorCallback): void
-  on(on: "message" | "error", cb: IncomingMessageCallback | ErrorCallback) {
-    if (on === "message") {
-      this.#msgCallback = cb as IncomingMessageCallback
-    } else if (on === "error") {
-      this.#errorCallback = cb as ErrorCallback
-    } else {
-      throw new Error(`unexpected input: ${on}`)
-    }
-  }
-
   send(msg: OutgoingMessage): void {
     if (this.#socket.readyState < WebSocket.OPEN) {
       this.#pending.push(msg)
@@ -84,11 +81,11 @@ export class Conn {
     try {
       this.#socket.send(serializeOutgoingMessage(msg), (err) => {
         if (err !== undefined && err !== null) {
-          this.#errorCallback?.(err)
+          this.#onError?.(err)
         }
       })
     } catch (err) {
-      this.#errorCallback?.(err)
+      this.#onError?.(err)
     }
   }
 
@@ -96,26 +93,87 @@ export class Conn {
     try {
       this.#socket.close()
     } catch (err) {
-      this.#errorCallback?.(err)
+      this.#onError?.(err)
     }
   }
+
+  static async #parseIncomingMessage(data: string): Promise<IncomingMessage> {
+    const json = parseJson(data)
+    if (!(json instanceof Array)) {
+      throw new ProtocolError(`incoming message is not an array: ${data}`)
+    }
+    if (json.length === 0) {
+      throw new ProtocolError(`incoming message is an empty array: ${data}`)
+    }
+    if (json[0] === "EVENT") {
+      if (typeof json[1] !== "string") {
+        throw new ProtocolError(
+          `second element of "EVENT" should be a string, but wasn't: ${data}`
+        )
+      }
+      if (typeof json[2] !== "object") {
+        throw new ProtocolError(
+          `second element of "EVENT" should be an object, but wasn't: ${data}`
+        )
+      }
+      const raw = parseEventData(json[2])
+      return {
+        kind: "event",
+        subscriptionId: new SubscriptionId(json[1]),
+        signed: await SignedEvent.verify(raw),
+        raw,
+      }
+    }
+    if (json[0] === "NOTICE") {
+      if (typeof json[1] !== "string") {
+        throw new ProtocolError(
+          `second element of "NOTICE" should be a string, but wasn't: ${data}`
+        )
+      }
+      return {
+        kind: "notice",
+        notice: json[1],
+      }
+    }
+    if (json[0] === "OK") {
+      if (typeof json[1] !== "string") {
+        throw new ProtocolError(
+          `second element of "OK" should be a string, but wasn't: ${data}`
+        )
+      }
+      if (typeof json[2] !== "boolean") {
+        throw new ProtocolError(
+          `third element of "OK" should be a boolean, but wasn't: ${data}`
+        )
+      }
+      if (typeof json[3] !== "string") {
+        throw new ProtocolError(
+          `fourth element of "OK" should be a string, but wasn't: ${data}`
+        )
+      }
+      return {
+        kind: "ok",
+        eventId: new EventId(json[1]),
+        ok: json[2],
+        message: json[3],
+      }
+    }
+    throw new ProtocolError(`unknown incoming message: ${data}`)
+  }
 }
 
 /**
  * A message sent from a relay to the client.
  */
-export type IncomingMessage = IncomingEvent | IncomingNotice
+export type IncomingMessage = IncomingEvent | IncomingNotice | IncomingOk
 
-export const enum IncomingKind {
-  Event,
-  Notice,
-}
+export type IncomingKind = "event" | "notice" | "ok"
 
 /**
  * Incoming "EVENT" message.
  */
 export interface IncomingEvent {
-  kind: IncomingKind.Event
+  kind: "event"
   subscriptionId: SubscriptionId
   signed: SignedEvent
   raw: RawEvent
@@ -125,10 +183,20 @@ export interface IncomingEvent {
  * Incoming "NOTICE" message.
  */
 export interface IncomingNotice {
-  kind: IncomingKind.Notice
+  kind: "notice"
   notice: string
 }
 
+/**
+ * Incoming "OK" message.
+ */
+export interface IncomingOk {
+  kind: "ok"
+  eventId: EventId
+  ok: boolean
+  message: string
+}
+
 /**
  * A message sent from the client to a relay.
  */
@@ -137,17 +205,13 @@ export type OutgoingMessage =
   | OutgoingOpenSubscription
   | OutgoingCloseSubscription
 
-export const enum OutgoingKind {
-  Event,
-  OpenSubscription,
-  CloseSubscription,
-}
+export type OutgoingKind = "event" | "openSubscription" | "closeSubscription"
 
 /**
  * Outgoing "EVENT" message.
  */
 export interface OutgoingEvent {
-  kind: OutgoingKind.Event
+  kind: "event"
   event: SignedEvent | RawEvent
 }
 
@@ -155,7 +219,7 @@ export interface OutgoingEvent {
  * Outgoing "REQ" message, which opens a subscription.
  */
 export interface OutgoingOpenSubscription {
-  kind: OutgoingKind.OpenSubscription
+  kind: "openSubscription"
   id: SubscriptionId
   filters: Filters[]
 }
@@ -164,13 +228,10 @@ export interface OutgoingOpenSubscription {
  * Outgoing "CLOSE" message, which closes a subscription.
  */
 export interface OutgoingCloseSubscription {
-  kind: OutgoingKind.CloseSubscription
+  kind: "closeSubscription"
   id: SubscriptionId
 }
 
-type IncomingMessageCallback = (message: IncomingMessage) => unknown
-type ErrorCallback = (error: unknown) => unknown
-
 interface RawFilters {
   ids?: string[]
   authors?: string[]
@@ -182,59 +243,18 @@ interface RawFilters {
   limit?: number
 }
 
-async function parseIncomingMessage(data: string): Promise<IncomingMessage> {
-  const json = parseJson(data)
-  if (!(json instanceof Array)) {
-    throw new ProtocolError(`incoming message is not an array: ${data}`)
-  }
-  if (json.length === 0) {
-    throw new ProtocolError(`incoming message is an empty array: ${data}`)
-  }
-  if (json[0] === "EVENT") {
-    if (typeof json[1] !== "string") {
-      throw new ProtocolError(
-        `second element of "EVENT" should be a string, but wasn't: ${data}`
-      )
-    }
-    if (typeof json[2] !== "object") {
-      throw new ProtocolError(
-        `second element of "EVENT" should be an object, but wasn't: ${data}`
-      )
-    }
-    const raw = parseEventData(json[2])
-    return {
-      kind: IncomingKind.Event,
-      subscriptionId: new SubscriptionId(json[1]),
-      signed: await SignedEvent.verify(raw),
-      raw,
-    }
-  }
-  if (json[0] === "NOTICE") {
-    if (typeof json[1] !== "string") {
-      throw new ProtocolError(
-        `second element of "NOTICE" should be a string, but wasn't: ${data}`
-      )
-    }
-    return {
-      kind: IncomingKind.Notice,
-      notice: json[1],
-    }
-  }
-  throw new ProtocolError(`unknown incoming message: ${data}`)
-}
-
 function serializeOutgoingMessage(msg: OutgoingMessage): string {
-  if (msg.kind === OutgoingKind.Event) {
+  if (msg.kind === "event") {
     const raw =
       msg.event instanceof SignedEvent ? msg.event.serialize() : msg.event
     return JSON.stringify(["EVENT", raw])
-  } else if (msg.kind === OutgoingKind.OpenSubscription) {
+  } else if (msg.kind === "openSubscription") {
     return JSON.stringify([
       "REQ",
       msg.id.toString(),
       ...serializeFilters(msg.filters),
     ])
-  } else if (msg.kind === OutgoingKind.CloseSubscription) {
+  } else if (msg.kind === "closeSubscription") {
     return JSON.stringify(["CLOSE", msg.id.toString()])
   } else {
     throw new Error(`invalid message: ${JSON.stringify(msg)}`)
diff --git a/packages/nostr/src/client/emitter.ts b/packages/nostr/src/client/emitter.ts
index 3c98021..2c9eb78 100644
--- a/packages/nostr/src/client/emitter.ts
+++ b/packages/nostr/src/client/emitter.ts
@@ -1,5 +1,6 @@
 import Base from "events"
-import { EventParams, Nostr } from "."
+import { Nostr, SubscriptionId } from "."
+import { EventId, RawEvent, SignedEvent } from "../event"
 
 /**
  * Overrides providing better types for EventEmitter methods.
@@ -11,6 +12,7 @@ export class EventEmitter extends Base {
     listener: RemoveListener
   ): this
   override addListener(eventName: "notice", listener: NoticeListener): this
+  override addListener(eventName: "ok", listener: OkListener): this
   override addListener(eventName: "error", listener: ErrorListener): this
   override addListener(eventName: "newListener", listener: ErrorListener): this
   override addListener(eventName: EventName, listener: Listener): this {
@@ -21,6 +23,7 @@ export class EventEmitter extends Base {
   override emit(eventName: "removeListener", listener: RemoveListener): boolean
   override emit(eventName: "event", params: EventParams, nostr: Nostr): boolean
   override emit(eventName: "notice", notice: string, nostr: Nostr): boolean
+  override emit(eventName: "ok", params: OkParams, nostr: Nostr): boolean
   override emit(eventName: "error", err: unknown, nostr: Nostr): boolean
   override emit(eventName: EventName, ...args: unknown[]): boolean {
     return super.emit(eventName, ...args)
@@ -34,6 +37,7 @@ export class EventEmitter extends Base {
   override listeners(eventName: "removeListener"): EventListener[]
   override listeners(eventName: "event"): EventListener[]
   override listeners(eventName: "notice"): NoticeListener[]
+  override listeners(eventName: "ok"): OkListener[]
   override listeners(eventName: "error"): ErrorListener[]
   override listeners(eventName: EventName): Listener[] {
     return super.listeners(eventName) as Listener[]
@@ -43,8 +47,9 @@ export class EventEmitter extends Base {
   override off(eventName: "removeListener", listener: RemoveListener): this
   override off(eventName: "event", listener: EventListener): this
   override off(eventName: "notice", listener: NoticeListener): this
+  override off(eventName: "ok", listener: OkListener): this
   override off(eventName: "error", listener: ErrorListener): this
-  override off(eventName: string, listener: Listener): this {
+  override off(eventName: EventName, listener: Listener): this {
     return super.off(eventName, listener)
   }
 
@@ -52,6 +57,7 @@ export class EventEmitter extends Base {
   override on(eventName: "removeListener", listener: RemoveListener): this
   override on(eventName: "event", listener: EventListener): this
   override on(eventName: "notice", listener: NoticeListener): this
+  override on(eventName: "ok", listener: OkListener): this
   override on(eventName: "error", listener: ErrorListener): this
   override on(eventName: EventName, listener: Listener): this {
     return super.on(eventName, listener)
@@ -61,6 +67,7 @@ export class EventEmitter extends Base {
   override once(eventName: "removeListener", listener: RemoveListener): this
   override once(eventName: "event", listener: EventListener): this
   override once(eventName: "notice", listener: NoticeListener): this
+  override once(eventName: "ok", listener: OkListener): this
   override once(eventName: "error", listener: ErrorListener): this
   override once(eventName: EventName, listener: Listener): this {
     return super.once(eventName, listener)
@@ -76,6 +83,7 @@ export class EventEmitter extends Base {
   ): this
   override prependListener(eventName: "event", listener: EventListener): this
   override prependListener(eventName: "notice", listener: NoticeListener): this
+  override prependListener(eventName: "ok", listener: OkListener): this
   override prependListener(eventName: "error", listener: ErrorListener): this
   override prependListener(eventName: EventName, listener: Listener): this {
     return super.prependListener(eventName, listener)
@@ -97,6 +105,7 @@ export class EventEmitter extends Base {
     eventName: "notice",
     listener: NoticeListener
   ): this
+  override prependOnceListener(eventName: "ok", listener: OkListener): this
   override prependOnceListener(
     eventName: "error",
     listener: ErrorListener
@@ -116,6 +125,7 @@ export class EventEmitter extends Base {
   ): this
   override removeListener(eventName: "event", listener: EventListener): this
   override removeListener(eventName: "notice", listener: NoticeListener): this
+  override removeListener(eventName: "ok", listener: OkListener): this
   override removeListener(eventName: "error", listener: ErrorListener): this
   override removeListener(eventName: EventName, listener: Listener): this {
     return super.removeListener(eventName, listener)
@@ -131,15 +141,40 @@ export class EventEmitter extends Base {
 
 // TODO Also add on: ("subscribed", subscriptionId) which checks "OK"/"NOTICE" and makes a callback?
 // TODO Also add on: ("ok", boolean, eventId) which checks "OK"/"NOTICE" and makes a callback?
-type EventName = "newListener" | "removeListener" | "event" | "notice" | "error"
+type EventName =
+  | "newListener"
+  | "removeListener"
+  | "event"
+  | "notice"
+  | "ok"
+  | "error"
+
 type NewListener = (eventName: EventName, listener: Listener) => void
 type RemoveListener = (eventName: EventName, listener: Listener) => void
 type EventListener = (params: EventParams, nostr: Nostr) => void
+type OkListener = (params: OkParams, nostr: Nostr) => void
 type NoticeListener = (notice: string, nostr: Nostr) => void
 type ErrorListener = (error: unknown, nostr: Nostr) => void
+
 type Listener =
   | NewListener
   | RemoveListener
   | EventListener
   | NoticeListener
+  | OkListener
   | ErrorListener
+
+// TODO Document this
+export interface EventParams {
+  signed: SignedEvent
+  subscriptionId: SubscriptionId
+  raw: RawEvent
+}
+
+// TODO Document this
+export interface OkParams {
+  eventId: EventId
+  relay: URL
+  ok: boolean
+  message: string
+}
diff --git a/packages/nostr/src/client/index.ts b/packages/nostr/src/client/index.ts
index 48be246..d83e189 100644
--- a/packages/nostr/src/client/index.ts
+++ b/packages/nostr/src/client/index.ts
@@ -1,7 +1,7 @@
 import { ProtocolError } from "../error"
 import { EventId, Event, EventKind, SignedEvent, RawEvent } from "../event"
 import { PrivateKey, PublicKey } from "../keypair"
-import { Conn, IncomingKind, OutgoingKind } from "./conn"
+import { Conn } from "./conn"
 import * as secp from "@noble/secp256k1"
 import { EventEmitter } from "./emitter"
 
@@ -46,42 +46,53 @@ export class Nostr extends EventEmitter {
       return
     }
 
+    const connUrl = new URL(url)
+
     // If there is no existing connection, open a new one.
-    const conn = new Conn(url)
-
-    // Handle messages on this connection.
-    conn.on("message", async (msg) => {
-      try {
-        if (msg.kind === IncomingKind.Event) {
-          this.emit(
-            "event",
-            {
-              signed: msg.signed,
-              subscriptionId: msg.subscriptionId,
-              raw: msg.raw,
-            },
-            this
-          )
-        } else if (msg.kind === IncomingKind.Notice) {
-          this.emit("notice", msg.notice, this)
-        } else {
-          throw new ProtocolError(`invalid message ${msg}`)
+    const conn = new Conn({
+      url: connUrl,
+      // Handle messages on this connection.
+      onMessage: (msg) => {
+        try {
+          if (msg.kind === "event") {
+            this.emit(
+              "event",
+              {
+                signed: msg.signed,
+                subscriptionId: msg.subscriptionId,
+                raw: msg.raw,
+              },
+              this
+            )
+          } else if (msg.kind === "notice") {
+            this.emit("notice", msg.notice, this)
+          } else if (msg.kind === "ok") {
+            this.emit(
+              "ok",
+              {
+                eventId: msg.eventId,
+                relay: connUrl,
+                ok: msg.ok,
+                message: msg.message,
+              },
+              this
+            )
+          } else {
+            throw new ProtocolError(`invalid message ${msg}`)
+          }
+        } catch (err) {
+          this.emit("error", err, this)
         }
-      } catch (err) {
-        this.emit("error", err, this)
-      }
-    })
-
-    // Forward connection errors to the error callbacks.
-    conn.on("error", (err) => {
-      this.emit("error", err, this)
+      },
+      // Forward errors on this connection.
+      onError: (err) => this.emit("error", err, this),
     })
 
     // Resend existing subscriptions to this connection.
     for (const [key, filters] of this.#subscriptions.entries()) {
       const subscriptionId = new SubscriptionId(key)
       conn.send({
-        kind: OutgoingKind.OpenSubscription,
+        kind: "openSubscription",
         id: subscriptionId,
         filters,
       })
@@ -145,7 +156,7 @@ export class Nostr extends EventEmitter {
         continue
       }
       conn.send({
-        kind: OutgoingKind.OpenSubscription,
+        kind: "openSubscription",
         id: subscriptionId,
         filters,
       })
@@ -167,7 +178,7 @@ export class Nostr extends EventEmitter {
         continue
       }
       conn.send({
-        kind: OutgoingKind.CloseSubscription,
+        kind: "closeSubscription",
         id: subscriptionId,
       })
     }
@@ -210,7 +221,7 @@ export class Nostr extends EventEmitter {
         event = await SignedEvent.sign(event, key)
       }
       conn.send({
-        kind: OutgoingKind.Event,
+        kind: "event",
         event,
       })
     }
@@ -289,10 +300,3 @@ export interface Filters {
   until?: Date
   limit?: number
 }
-
-// TODO Document this
-export interface EventParams {
-  signed: SignedEvent
-  subscriptionId: SubscriptionId
-  raw: RawEvent
-}
diff --git a/packages/nostr/src/event.ts b/packages/nostr/src/event.ts
index 5dd4e02..8dcfb29 100644
--- a/packages/nostr/src/event.ts
+++ b/packages/nostr/src/event.ts
@@ -87,7 +87,8 @@ export class EventId {
     }
   }
 
-  private constructor(hex: string) {
+  constructor(hex: string) {
+    // TODO Validate that this is 32-byte hex
     this.#hex = hex
   }
 
diff --git a/packages/nostr/test/simple-communication.ts b/packages/nostr/test/simple-communication.ts
index 86c6618..4841a6e 100644
--- a/packages/nostr/test/simple-communication.ts
+++ b/packages/nostr/test/simple-communication.ts
@@ -1,26 +1,37 @@
-import { EventParams, Nostr } from "../src/client"
-import { EventKind } from "../src/event"
+import { Nostr } from "../src/client"
+import { EventKind, SignedEvent } from "../src/event"
 import { PrivateKey } from "../src/keypair"
 import assert from "assert"
+import { EventParams } from "../src/client/emitter"
 
 // TODO Switch out the relay implementation and see if the issue persists
+// TODO Do on("error", done) for all of these
 
-describe("single event communication", function () {
-  it("ok", function (done) {
-    const secret = new PrivateKey(
-      "nsec1xlu55y6fqfgrq448xslt6a8j2rh7lj08hyhgs94ryq04yf6surwsjl0kzh"
-    )
-    const pubkey = secret.pubkey
+describe("simple communication", function () {
+  const secret = new PrivateKey(
+    "nsec1xlu55y6fqfgrq448xslt6a8j2rh7lj08hyhgs94ryq04yf6surwsjl0kzh"
+  )
+  const pubkey = secret.pubkey
+  const timestamp = new Date()
+  const note = "hello world"
+  const url = new URL("ws://localhost:12648")
 
-    const timestamp = new Date()
-    const note = "hello world"
+  const publisher = new Nostr()
+  const subscriber = new Nostr()
 
-    const publisher = new Nostr()
-    publisher.open("ws://localhost:12648")
-    const subscriber = new Nostr()
-    subscriber.open("ws://localhost:12648")
+  beforeEach(() => {
+    publisher.open(url)
+    subscriber.open(url)
+  })
 
-    function listener({ signed: { event } }: EventParams) {
+  afterEach(() => {
+    publisher.close()
+    subscriber.close()
+  })
+
+  it("publish and receive", function (done) {
+    function listener({ signed: { event } }: EventParams, nostr: Nostr) {
+      assert.equal(nostr, subscriber)
       assert.equal(event.kind, EventKind.TextNote)
       assert.equal(event.pubkey.toString(), pubkey.toString())
       assert.equal(event.createdAt.toString(), timestamp.toString())
@@ -34,16 +45,11 @@ describe("single event communication", function () {
       // for future events.
       subscriber.off("event", listener)
 
-      publisher.close()
-      subscriber.close()
-
       done()
     }
 
     subscriber.on("event", listener)
-
     subscriber.subscribe([])
-
     publisher.publish(
       {
         kind: EventKind.TextNote,
@@ -54,4 +60,26 @@ describe("single event communication", function () {
       secret
     )
   })
+
+  it("publish and ok", function (done) {
+    SignedEvent.sign(
+      {
+        kind: EventKind.TextNote,
+        createdAt: timestamp,
+        content: note,
+        pubkey,
+      },
+      secret
+    ).then((event) => {
+      publisher.on("ok", (params, nostr) => {
+        assert.equal(nostr, publisher)
+        assert.equal(params.eventId.toString(), event.eventId.toString())
+        assert.equal(params.relay.toString(), url.toString())
+        assert.equal(params.ok, true)
+        done()
+      })
+      publisher.on("error", done)
+      publisher.publish(event)
+    })
+  })
 })