diff --git a/README.md b/README.md
index cd5221e..5193757 100644
--- a/README.md
+++ b/README.md
@@ -158,6 +158,11 @@ let events = await pool.list(relays, [{kinds: [0, 1]}])
 let event = await pool.get(relays, {
   ids: ['44e1827635450ebb3c5a7d12c1f8e7b2b514439ac10a67eef3d9fd9c5c68e245']
 })
+
+let relaysForEvent = pool.seenOn(
+  '44e1827635450ebb3c5a7d12c1f8e7b2b514439ac10a67eef3d9fd9c5c68e245'
+)
+// relaysForEvent will be an array of URLs from relays a given event was seen on
 ```
 
 ### Querying profile data from a NIP-05 address
diff --git a/package.json b/package.json
index b81ab91..a35e7b0 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "nostr-tools",
-  "version": "1.3.1",
+  "version": "1.3.2",
   "description": "Tools for making a Nostr client.",
   "repository": {
     "type": "git",
diff --git a/pool.test.js b/pool.test.js
index 1c6805f..2a23830 100644
--- a/pool.test.js
+++ b/pool.test.js
@@ -20,7 +20,12 @@ let relays = [
 ]
 
 afterAll(async () => {
-  await pool.close([...relays, 'wss://nostr-relay.untethr.me'])
+  await pool.close([
+    ...relays,
+    'wss://nostr-relay.untethr.me',
+    'wss://offchain.pub',
+    'wss://eden.nostr.land'
+  ])
 })
 
 test('removing duplicates when querying', async () => {
@@ -120,4 +125,9 @@ test('list()', async () => {
       .reduce((acc, n) => (acc.indexOf(n) !== -1 ? acc : [...acc, n]), [])
       .length
   )
+
+  let relaysForAllEvents = events
+    .map(event => pool.seenOn(event.id))
+    .reduce((acc, n) => acc.concat(n), [])
+  expect(relaysForAllEvents.length).toBeGreaterThanOrEqual(events.length)
 })
diff --git a/pool.ts b/pool.ts
index b8256b3..6ecf469 100644
--- a/pool.ts
+++ b/pool.ts
@@ -6,10 +6,10 @@ import {SubscriptionOptions, Sub, Pub} from './relay'
 
 export class SimplePool {
   private _conn: {[url: string]: Relay}
+  private _seenOn: {[id: string]: Set<string>} = {} // a map of all events we've seen in each relay
 
-  constructor(defaultRelays: string[] = []) {
+  constructor() {
     this._conn = {}
-    defaultRelays.forEach(this.ensureRelay)
   }
 
   async close(relays: string[]): Promise<void> {
@@ -37,7 +37,12 @@ export class SimplePool {
   sub(relays: string[], filters: Filter[], opts?: SubscriptionOptions): Sub {
     let _knownIds: Set<string> = new Set()
     let modifiedOpts = opts || {}
-    modifiedOpts.alreadyHaveEvent = id => _knownIds.has(id)
+    modifiedOpts.alreadyHaveEvent = (id, url) => {
+      let set = this._seenOn[id] || new Set()
+      set.add(url)
+      this._seenOn[id] = set
+      return _knownIds.has(id)
+    }
 
     let subs: Sub[] = []
     let eventListeners: Set<(event: Event) => void> = new Set()
@@ -47,9 +52,7 @@ export class SimplePool {
     let eoseSent = false
     let eoseTimeout = setTimeout(() => {
       eoseSent = true
-      for (let cb of eoseListeners.values()) {
-        cb()
-      }
+      for (let cb of eoseListeners.values()) cb()
     }, 2400)
 
     relays.forEach(async relay => {
@@ -58,9 +61,7 @@ export class SimplePool {
       let s = r.sub(filters, modifiedOpts)
       s.on('event', (event: Event) => {
         _knownIds.add(event.id as string)
-        for (let cb of eventListeners.values()) {
-          cb(event)
-        }
+        for (let cb of eventListeners.values()) cb(event)
       })
       s.on('eose', () => {
         if (eoseSent) return
@@ -68,9 +69,7 @@ export class SimplePool {
         eosesMissing--
         if (eosesMissing === 0) {
           clearTimeout(eoseTimeout)
-          for (let cb of eoseListeners.values()) {
-            cb()
-          }
+          for (let cb of eoseListeners.values()) cb()
         }
       })
       subs.push(s)
@@ -85,9 +84,14 @@ export class SimplePool {
         subs.forEach(sub => sub.unsub())
       },
       on(type, cb) {
-        if (type === 'event') {
-          eventListeners.add(cb)
-        } else if (type === 'eose') eoseListeners.add(cb)
+        switch (type) {
+          case 'event':
+            eventListeners.add(cb)
+            break
+          case 'eose':
+            eoseListeners.add(cb)
+            break
+        }
       },
       off(type, cb) {
         if (type === 'event') {
@@ -147,6 +151,10 @@ export class SimplePool {
       return s
     })
   }
+
+  seenOn(id: string): string[] {
+    return Array.from(this._seenOn[id]?.values?.() || [])
+  }
 }
 
 function badPub(relay: string): Pub {
diff --git a/relay.ts b/relay.ts
index 5e6fea7..7593cef 100644
--- a/relay.ts
+++ b/relay.ts
@@ -30,9 +30,9 @@ export type Sub = {
 }
 
 export type SubscriptionOptions = {
-  skipVerification?: boolean
-  alreadyHaveEvent?: null | ((id: string) => boolean)
   id?: string
+  skipVerification?: boolean
+  alreadyHaveEvent?: null | ((id: string, relay: string) => boolean)
 }
 
 export function relayInit(url: string): Relay {
@@ -112,7 +112,7 @@ export function relayInit(url: string): Relay {
           if (
             so &&
             so.alreadyHaveEvent &&
-            so.alreadyHaveEvent(getHex64(json, 'id'))
+            so.alreadyHaveEvent(getHex64(json, 'id'), url)
           ) {
             return
           }