diff --git a/abstract-relay.ts b/abstract-relay.ts
index 4579b7f..e8c88de 100644
--- a/abstract-relay.ts
+++ b/abstract-relay.ts
@@ -331,13 +331,23 @@ export class AbstractRelay {
           so.close(data[2] as string)
           return
         }
-        case 'NOTICE':
+        case 'NOTICE': {
           this.onnotice(data[1] as string)
           return
+        }
         case 'AUTH': {
           this.challenge = data[1] as string
           return
         }
+        case 'NEG-ERR':
+        case 'NEG-MSG': {
+          const msg = data[2] as string
+          const id = data[1] as string
+          const so = this.openSubs.get(id)
+          if (!so || !so.onnegentropy) return
+          so.onnegentropy(msg, data[0] === 'NEG-ERR')
+          return
+        }
       }
     } catch (err) {
       return
@@ -404,9 +414,12 @@ export class AbstractRelay {
   public subscribe(
     filters: Filter[],
     params: Partial<SubscriptionParams> & { label?: string; id?: string },
+    fireImmediately: boolean = true,
   ): Subscription {
     const subscription = this.prepareSubscription(filters, params)
-    subscription.fire()
+    if (fireImmediately) {
+      subscription.fire()
+    }
     return subscription
   }
 
@@ -459,6 +472,7 @@ export class Subscription {
   public alreadyHaveEvent: ((id: string) => boolean) | undefined
   public receivedEvent: ((relay: AbstractRelay, id: string) => void) | undefined
 
+  public onnegentropy: ((msg: string, isError: boolean) => void) | undefined
   public onevent: (evt: Event) => void
   public oneose: (() => void) | undefined
   public onclose: ((reason: string) => void) | undefined
@@ -474,6 +488,7 @@ export class Subscription {
     this.receivedEvent = params.receivedEvent
     this.eoseTimeout = params.eoseTimeout || relay.baseEoseTimeout
 
+    this.onnegentropy = params.onnegentropy
     this.oneose = params.oneose
     this.onclose = params.onclose
     this.onevent =
@@ -523,6 +538,7 @@ export class Subscription {
 export type SubscriptionParams = {
   onevent?: (evt: Event) => void
   oneose?: () => void
+  onnegentropy?: (msg: string, isError: boolean) => void
   onclose?: (reason: string) => void
   alreadyHaveEvent?: (id: string) => boolean
   receivedEvent?: (relay: AbstractRelay, id: string) => void
diff --git a/helpers.ts b/helpers.ts
index 3457fda..56d5df0 100644
--- a/helpers.ts
+++ b/helpers.ts
@@ -1,17 +1,34 @@
 import { verifiedSymbol, type Event, type Nostr, VerifiedEvent } from './core.ts'
 
 export async function yieldThread() {
-  return new Promise<void>(resolve => {
-    const ch = new MessageChannel()
-    const handler = () => {
-      // @ts-ignore (typescript thinks this property should be called `removeListener`, but in fact it's `removeEventListener`)
-      ch.port1.removeEventListener('message', handler)
-      resolve()
+  return new Promise<void>((resolve, reject) => {
+    try {
+      // Check if MessageChannel is available
+      if (typeof MessageChannel !== 'undefined') {
+        const ch = new MessageChannel()
+        const handler = () => {
+          // @ts-ignore (typescript thinks this property should be called `removeListener`, but in fact it's `removeEventListener`)
+          ch.port1.removeEventListener('message', handler)
+          resolve()
+        }
+        // @ts-ignore (typescript thinks this property should be called `addListener`, but in fact it's `addEventListener`)
+        ch.port1.addEventListener('message', handler)
+        ch.port2.postMessage(0)
+        ch.port1.start()
+      } else {
+        if (typeof setImmediate !== 'undefined') {
+          setImmediate(resolve)
+        } else if (typeof setTimeout !== 'undefined') {
+          setTimeout(resolve, 0)
+        } else {
+          // Last resort - resolve immediately
+          resolve()
+        }
+      }
+    } catch (e) {
+      console.error('during yield: ', e)
+      reject(e)
     }
-    // @ts-ignore (typescript thinks this property should be called `addListener`, but in fact it's `addEventListener`)
-    ch.port1.addEventListener('message', handler)
-    ch.port2.postMessage(0)
-    ch.port1.start()
   })
 }
 
diff --git a/index.ts b/index.ts
index 69aef00..ea77374 100644
--- a/index.ts
+++ b/index.ts
@@ -24,6 +24,7 @@ export * as nip47 from './nip47.ts'
 export * as nip54 from './nip54.ts'
 export * as nip57 from './nip57.ts'
 export * as nip59 from './nip59.ts'
+export * as nip77 from './nip77.ts'
 export * as nip98 from './nip98.ts'
 
 export * as kinds from './kinds.ts'
diff --git a/nip77.test.ts b/nip77.test.ts
new file mode 100644
index 0000000..13479b5
--- /dev/null
+++ b/nip77.test.ts
@@ -0,0 +1,91 @@
+import { describe, it, expect } from 'bun:test'
+
+import { sendNegentropyMessage, openNegentropyWithMessage, closeNegentropy } from './nip77.ts'
+import type { Filter } from './filter.ts'
+import { AbstractRelay } from './abstract-relay.ts'
+import type { Event, VerifiedEvent } from './core.ts'
+
+// A minimal mock relay implementing send(). We don't need websocket behavior here.
+class MockRelay extends AbstractRelay {
+  public sent: string[] = []
+  constructor(url: string = 'wss://example.com') {
+    // pass a dummy verifyEvent function to satisfy constructor (always returns true)
+    const verifyEvent = (event: Event): event is VerifiedEvent => true
+    super(url, { verifyEvent })
+    // Pretend it's connected so send() doesn't throw.
+    // @ts-ignore accessing private
+    this.connectionPromise = Promise.resolve()
+  }
+  public override async send(message: string) {
+    this.sent.push(message)
+  }
+}
+
+function extractJSON(message: string) {
+  return JSON.parse(message)
+}
+
+describe('nip77 negentropy message helpers', () => {
+  it('sendNegentropyMessage should send NEG-MSG with generated subscription id and filters flattened', () => {
+    const relay = new MockRelay()
+    const filters: Filter[] = [
+      { kinds: [1], authors: ['abc'] },
+      { ids: ['deadbeef'] },
+    ]
+    sendNegentropyMessage(relay as any, 'hello', filters)
+
+    expect(relay.sent.length).toBe(1)
+    const arr = extractJSON(relay.sent[0])
+    expect(arr[0]).toBe('NEG-MSG')
+    expect(typeof arr[1]).toBe('string') // auto sub id
+    // message should include each filter object fields flattened after the sub id
+    // Request format built in nip77.ts: ["NEG-MSG","subId",<filters without outer []>,"msg"]
+    // So positions 2..n-2 are filter objects; last element is the msg string
+    expect(arr[arr.length - 1]).toBe('hello')
+    // Ensure at least one property from each filter is present
+    const serialized = relay.sent[0]
+    expect(serialized.includes('"kinds":[1]')).toBe(true)
+    expect(serialized.includes('"authors":["abc"]')).toBe(true)
+    expect(serialized.includes('"ids":["deadbeef"]')).toBe(true)
+  })
+
+  it('openNegentropyWithMessage should send NEG-OPEN', () => {
+    const relay = new MockRelay()
+    const filters: Filter[] = [{ kinds: [3] }]
+    openNegentropyWithMessage(relay as any, 'init', filters, 'sub123')
+
+    expect(relay.sent.length).toBe(1)
+    const arr = extractJSON(relay.sent[0])
+    expect(arr[0]).toBe('NEG-OPEN')
+    expect(arr[1]).toBe('sub123')
+    expect(arr[arr.length - 1]).toBe('init')
+  })
+
+  it('closeNegentropy should send NEG-CLOSE with given subscription id', () => {
+    const relay = new MockRelay()
+    closeNegentropy(relay as any, 'subXYZ')
+
+    expect(relay.sent.length).toBe(1)
+    const arr = extractJSON(relay.sent[0])
+    expect(arr).toEqual(['NEG-CLOSE', 'subXYZ'])
+  })
+
+  it('sendNegentropyMessage should honor provided subscriptionId', () => {
+    const relay = new MockRelay()
+    const filters: Filter[] = [{ kinds: [1] }]
+    sendNegentropyMessage(relay as any, 'custom', filters, 'customSub')
+    const arr = extractJSON(relay.sent[0])
+    expect(arr[1]).toBe('customSub')
+  })
+
+  it('should handle empty filters array (request still valid)', () => {
+    const relay = new MockRelay()
+    sendNegentropyMessage(relay as any, 'nofilters', [])
+    const arr = extractJSON(relay.sent[0])
+    expect(arr[0]).toBe('NEG-MSG')
+    expect(typeof arr[1]).toBe('string')
+    // With empty filters array we expect exactly 3 elements: type, subId, msg
+    expect(arr.length).toBe(3)
+    expect(arr[2]).toBe('nofilters')
+  })
+})
diff --git a/nip77.ts b/nip77.ts
new file mode 100644
index 0000000..9c83ec5
--- /dev/null
+++ b/nip77.ts
@@ -0,0 +1,21 @@
+import { Filter } from './filter.ts'
+import { AbstractRelay } from './relay.ts'
+
+function sendNegentropyToRelay(open: boolean, relay: AbstractRelay, msg: string, filters: Filter[], subscriptionId?: any): void {
+  const subId = subscriptionId || Math.random().toString(36).slice(2, 10)
+  const parts: any[] = [open ? 'NEG-OPEN' : 'NEG-MSG', subId, ...filters, msg]
+  relay.send(JSON.stringify(parts))
+}
+
+export function sendNegentropyMessage(relay: AbstractRelay, msg: string, filters: Filter[], subscriptionId?: any): void {
+  sendNegentropyToRelay(false, relay, msg, filters, subscriptionId)
+}
+
+export function openNegentropyWithMessage(relay: AbstractRelay, msg: string, filters: Filter[], subscriptionId?: any): void {
+  sendNegentropyToRelay(true, relay, msg, filters, subscriptionId)
+}
+
+export function closeNegentropy(relay: AbstractRelay, subscriptionId: string): void {
+  const request = '["NEG-CLOSE","' + subscriptionId + '"]'
+  relay.send(request)
+}